Propellor Q & A

I have a 1984 Hunter 34' sailboat. Installing a new engine, Yanmar 3ym30 (29 HP). What size prop would you recommend? I'm strictly a coastal cruiser and would like a 3 blade. What are your thoughts? Carl W.

Hi Carl: There are too many variables to do this off the cuff. These include boat characteristics, engine prop curve, transmission reduction, and the type of prop (feathering, folding, two blade, or three blade). Best bet is to talk with a prop shop in your area that is familiar with the boat. There is also a large section in our Offshore Cruising Encyclopedia on propellers, which might help you in making a choice. Regards - Steve

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Dear Steve,

I am building a Bruce Roberts kit of 54' radius chine cutter. After reading the Offshore Cruising Encyclopedia and viewing your Beowulf: The Legend DVD, I have decided to install CP prop by Hundested. I am getting the prop from Todd Terry at Pacific Marine Equipment, Inc. in Seattle. As far as I was able to find out, they are the (US) West Coast distributor for Hundested gear. Anyway, the thing is: You are saying in your book that you were using VP2 model, which according to Todd is no longer available. Therefore I am going with a bit larger VP3 model. Now, according to Todd, one can choose either fully reversible pitch prop or fully featherable prop to minimize the drag while sailing.

If I choose fully featherable prop, my reverse pitch is very minimal, nowhere near the forward pitch. If I choose the fully reversible prop I will have to give up the low drag feature of fully feathered prop.

After viewing Beowulf DVD In the chapter titled "Maneuvering Under Power", you have Linda reverse the pitch from 3.5 ahead to 4 astern. The scale on the gauge shows up to 6 ahead, up to 5 astern and also feathered position. Does it mean that with the VP2 you had the option of having nearly fully reversible pitch and also feathered position for sailing???

Are you familiar with the VP3 model and what is the difference between it and the old VP2 one? I have seen the operational model of VP3 in Seattle and in fact the reverse pitch is very minimal, a fraction of the forward pitch capabilities. Was your prop the same way?

I am sorry for rumbling on and on about it, but the Hundested props as you know are not cheap and I would like to make sure that my money will be wisely spent. I would be very grateful for your comments regarding this matter.

Good luck with your UnSailboat! I hope to meet you one day in some anchorage. Best Regards, Remek

Hi Remek: Either the distributor is telling you something that is incorrect or Hundested has changed something.

To begin with, on BEOWULF, we had both good reverse capability and full feathering. The blades would not go as far in reverse as they did forward, but it was more than sufficient for stopping the boat and for walking it around a circle using prop torque (in either direction). The model we ordered was specified as full feathering. This VP2 was purchased in about 1993, and I they could probably check their records at Hundested.

As to the VP3, this is a very much larger hub, and if your engine is not large enough to take advantage of the larger hub and blades, then I would re-think the use of the Hundested. We used a VP3 on Kondor, similar to BEOWULF except she was a little heavier and had a 225HP Yanmar instead of the 170 HP which we had on BEOWULF. I believe her prop diameter was 27" or 28" BEOWULF was 26".

If your engine is under 185HP, then I would probably pay the efficiency penalty of something like a 3-bladed Max prop, and think about over-pitching to reduce face cavitation on the Max prop (discussion of this in Offshore Cruising Encyclopedia). Good Luck--Steve

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Hi! My dealer and I are having this contest, you know the kind ;) about painting the prop shaft and prop. He's already done it, and insists it's "always done that way." I say no. I want the paint removed.

The vessel is a 2000 Hunter Passage 450, the prop is an Autoprop. The Autoprop dealer (A&B Marine) recommends not painting but using their "Anti-Fouling Goop," a greasy lanolin compound.

I have had to scrape the barnacles off the prop personally, so I know that bottom paint does not retard marine growth here in SW Florida. The Goop "seems" to work. It's not been tried on a clean prop over an entire season.

Comments?

I love the books, videos, CDs and am amazed with MaxSea, especially the weather routing.

Keep sailing! Errrr...... Boating!!!!!! Regards, Drew D

Hi Drew: I have tested many paint systems on props over the years and not found one that works. In fact, some of the paint usually falls off in a short time leaving a rough, inefficient finish on the prop. So, I agree with you, take it off. I'd love to know more about your "goop", what it is, and how it works. Steve

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What effect is there on propeller performance and vibration when fitted in the opposite rotation to that recommended by the boat builder?

I just purchased a 9 year old Grand Soleil Maxi One (19.5m) and am having a lot of problems with engine & MaxProp giving a lot of very bad vibrations and engine not being able to obtain correct cruising revs (should be about 2700/2800 rpm--and getting black smoke when revving above 2200rpm).

Obvious answer is the prop is over pitched. However, on checking with MaxProp rep here in Athens, he just serviced and refitted the prop with 20 degs with right rotation. According to the Manual on board from the builders (Canteir del Pardo) the prop should be 14 degs--Left Rotation.

Of course the over pitching of the prop answers the problem of the engine not revving etc, but would the wrong rotation cause increasingly bad vibrations the more rpm's applied?

I need some urgent advice because the incorrect running of the engine over the last 8/9 years (by previous owner) has caused all sorts of problems including overheating, broken pipe in heat exchanger and blown gasket leading to water into the cylinders and turbo etc on my recent outing with service engineers on board testing the engine after service. Thus, decided to put new engine as do not want to have further trouble/time/expense of trying to renew/overhaul existing engine.

Obviously have to find also a solution for the bad vibrations, but I cannot get Maxprop or del Pardo to reply to my emails and faxes.

Hi George:

I'll try to help.

1-Max Props work the same in both directions since they do not have any airfoil shape.

2-Some transmissions can be used in both directions as well, sometimes with a very slight difference in reduction gear. When this is the case, you chose the rotation direction so that you get stern walk in the best direction for how you normally dock (or dock most often).

3-Assuming your transmission can be used ahead in both directions, you then can consider which way to pitch the prop. If you allow the engine to develop full rpms, with high speed engines and Max props you typically have some face cavitation--which makes the prop less effective. However, if you over-prop, you have to be very careful not to overload the engine. There is a chapter on this subject in our Offshore Cruising Encyclopedia.

4-The vibration could be coming from a bent prop shaft--it only takes a tiny bend to vibrate like crazy. It could be coming from an alignment problem. Or the prop itself could be out of balance. You can check for a bent shaft out of the water by rotating the shaft and sighting carefully for a big bend. Small bends need to be checked in a machine shop.

5-I would do the following in this order:

A-Verify the transmission can be run in both directions. If not, correct the direction of rotation for the prop (and change your shift cables accordingly!).
B-Check prop shaft flange to transmission alignment.
C-Make sure the prop is clean.
D-Verify the prop is balanced and the prop shaft is not bent.

Good Luck--Steve

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I wonder if you have any opinion on electric propulsion? I am considering re-powering with a Solomon system. I have a 30hp Westerbeke diesel at this point. I am cruising full time with lots of hours at anchor. Comparing prices, diesel/electric, is a definite apples/oranges situation, with the result being that I may decide based on my dislike of the internal combustion engine. Certainly would appreciate your reaction to the this concept used in a cruising sailboat. Ross

Hi Ross: I have no direct experience with diesel electric. However, the concept is sound--many commercial and navy ships are powered this way. The key with taking advantage with a sailboat is prop efficiency. I.e. the ability to turn a large prop slowly. But of course this brings in other issues like prop drag (even if it is as folder or feathering), tip clearance, etc. Let us know how it turns out of you go this route. Some before and after data would be great! Steve

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Dear Steve, I have a Kelly Peterson 46 with a fixed 3-blade prop. I want to change it to a feathering prop. I am intrigued by the continuously adjusting Autoprop which is supposed to match pitch to engine rpm and twist more or less flat to cut drag under sail to 85% of a fixed blade prop. I wonder what happens to the independently adjusting blades when barnacles form and they become unbalanced. Maxprop has less drag under sail but its pitch is optimized for max rpm and falls off (like fixed props) at lower engine rpm. Do you know how well these things work in the field? Any kudos or horror stories. Thanks, Carl

Hi Carl: Whatever you decide on, you will get a hhuge boost in sailing performance, and probably some help under power too. Re: Autoprop, I have no direct experience. I know a lot of their users like them. There are some maintenance issues with bearings and underwater growth, but they do not seem to be insurmountable. Max Prop is probably better in reverse, not as good forward, but will have less drag under sail. Best thing to do is find folks with Peterson 44/46s that have real world experience and compare. Let us know what you learn. Steve

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Steve, I was fortunate to have sailed with you and Linda in Ventura a number of years ago and got to back your boat into the slip easily due to the max-prop. I need to decide between a max-prop and a controllable pitch prop. It seems that the max-prop might have the advantage in backing where the cpp shines due to ease of adjustment underway. Which do you prefer and why? Robert

Hi Robert: Tough question. As far as backing goes, you can reduce pitch on the CP prop and it will go straight in reverse. Or, you can walk the stern in iether direction--a huge advantage. And then it is is about 50% more efficient under power than Max Props.

On the negative side, way more expensive, much heavier, and draggy with twisted blades and big hub (which is why it is so efficient). I could go either way as I would put up with lack of maneuverability which comes with Max Prop for better sailing. But Linda puts the Hundested in the same category as the washer/drier. She isn't going cruising without either one. Steve

Hey Steve, Thanks for the reply about the cpp prop setup. I have a follow-up question. There generally seems to be 2 different basic types of cpp setups, one is a reversible marine gear and separate pitch controller (ie. smaller Hundested), the other has the reduction and pitch together with the shaft turning only one direction (larger Hundested, Sabb, Finnoy, etc.). Do you see an advantage to either system? Also I have to either provide a washer/dryer or sail alone. Is it reasonable to run it off an inverter or is a genset required? Thanks.

Having both a CP prop and trasmission allows you to walk the stern in either direction. This is a huge advantage and 80% of the reason to have the CP in the first place! You can always rotate in either dorection, and pull the stern on or off the dock (or away from an obstruction) regardless of which way the boat is lying. Running a washer/drier on a 2400 watt inverter is no big deal. But you might want to run the engine at the same time to keep batteries up--unless you have a large battery bank. On BEOWULF, we frequently do one or two washes without the engine, but then she has 800 usable amp hours at 24 volts.- Steve

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In your very valuable Encyclopedia (looking forward to read the heavy weather issue) you briefly mentioned a way to generate DC power with a MAXPROP or AUTOPROP. Is there any description available on this setup? My boat is a Gerard Dijkstra designed 77 ft centerboard shooner (steel, 60 tons) and a MAXPROP is fitted but I am thinking of changing to AUTOPROP (only for performance when maneuvering). Is it possible to do the same trick with this prop? I hope you find the time for an answer. Best regards, Paul

Hi Paul: With a Maxi Prop you shut the engine down while it is running in reverse. The blades usually stay reversed and do not feather, so the shaft turns and you can generate power. When you want to feather the blades start the engine, put it into forward gear, and then stop and the prop will feather normally.

One comment about using the main prop in general for power--it tends to be noisy, although if you only need it for a couple of hours a day it is probably less of a bother than streaming something over the stern which is going 24 hours a day!

If you make the switch to the Autoprop let us know how it turns out. I'd love to know the difference in speed, fuel consumption, reversing, and how the stern reacts when you back down. Regards --Steve

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Question: I was going to install a feathing prop on my Nautic Saintongue 44 during this spring's haul-out. Presently, I have postponed this investment because I met a couple in La Paz this winter who had a feathering prop on a Passport about the same displacement as my boat. I asked them if the prop (maxi) was working for them. They replied that if they had to consider it again, they would not do it again. Basicially it was not worth the investment.

So, what is your opinion on replacing a fixed three blade with a maxi type prop? From manufacturers reports I have read, an increase in speed will be realized, but on a 25,000 lb. displacement boat, is the investment worth it? I do not race, but like to get from one place to the next as quickly as possible.

What prop has worked best for your boats over the years? Mike

Hi Mike: A good question, which hinges on your definition of what some speed and maneuverability is worth.

Leaving aside the issue of which feathering prop for the moment, a three bladed fixed prop creates a huge amount of drag. This has the biggest negative impact in light airs and when sailing to windward. It also has relatively poor handling characteristics when going in reverse (i.e. they tend to circle regardless of what you do on the helm unless you are very lucky, or skilled--or both).

So switching to a more efficient prop for sailing allows you to go faster. How important is this? Let's leave aside the issue of the pleasure to be had in sailing fast and concentrate on safety. If you average 15/20 miles a day more on a passage because you've switched props (easy to do in your situation) that means the passage is over three to four hours sooner for each day at sea. If you are racing to port, to beat the arrival of a nasty depression, this could make the difference. Or, you might be trying to make it through a particular coral pass or harbor entrance with the light over your shoulder--again the extra speed gives you a margin of safety.

And heaven forbid you should ever be caught on a lee shore, fighting your way to weather in a real blow, getting rid of the fixed prop will make a huge difference in your VMG.

So, I feel strongly that there is a big increase in safety factors to be had in this change. Is it worth three to six months of cruising budget? That is a harder call to make.

Now, as to the specific aproach, there are a number of feathering wheels on the market--The Max Prop of couse, and the Bruntan's sef pitching prop. And don't forget to look at Martec too. Occasionally you can find used versions of these. We've had lots of experience with Max props, and within the caveats discussed at length in Offshore Cruising Encyclopedia--they work well.

If you change let us know what you think of the difference. Regards --Steve Dashew

An Update:

Hi Steve: Just wanted to get back to you on your answer to my question a while back about fix props and feathering props. I replaced a 3 blade fixed prop on my 44 foot sloop IOR design boat with a max prop. You were certainly right about the speed increase under sail, the prices was worth the performance alone. Also, backing is better, since prop walk is gone. So far only draw back is getting the right pitch setting. The factory rep suggested a setting of K E, which has not allowed maximum rpm, infact the engine overheated for the first time trying to reach what I did before 2950 rpms with the fixed 17X12. I could only do 2500 rpms with the max set at 18X12.4. So now I will be setting an EH (18X11) to improve max speed. So, the draw back is another haulout and $280 invested. Wounder if I should have bought their adjustable VP model?

Thanks for your help. Mike

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I replaced my fixed prop ( 3-blade 16 RH 10) with a 17 RH 10 Flex-O-Fold 2-blade folding prop. I have experienced much improved speed under sail and not bad performance in reverse. However, I am unable to get full cruising RPM in forward and because of this am not able to motor cruise at much more than 4.3 knots. My vessel is a Nautilus 37 with a 35 hp Yanmar diesel. Also I am experiencing vibration at 1900 RPM which I did not have with my fixed prop. Any suggestions? Ron

Hi Ron: The first step would be to go back to the prop supplier and have some dialog. Sounds like you've got a bit too much blade diameter or pitch. This could be the result of improperly reading the reduction gear data- i.e., if the reduction gear has less of a reduction ratio, the prop would be spinning faster, which would cause the problem you're encountering. Good Luck--Steve

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Hi again. We are in the process of installing a diesel engine in our Mirage. All was going according to plan, until a fellow boater mentioned crabbing, and warned us that placement of the prop is critical. If not offset, the boat will 'crab', worse in reverse, than in forward. Next Saturday, the hole is being cut through the hull. I've had a look through the Encyclopedia, but can't find much about proper placement of the shaft/prop, and although many of my boating friends have heard of it, no one can elaborate. I've looked at the last few boats in the area that are still out of the water, and find that the shaft is placed dead-centre. Do you have any advice, or do you have a publication that explains the concept? Your help is appreciated. Jim from Canada

Jim: In the olden days, the norm on full keel, attached rudder boats, props was to offset the prop so the builder would not have to cut away the rudder or trailing edge of the keel (and so that the prop shaft and required bearings was an easier installation).

These had to be done so that the offset would be counteracted to some degree by the somewhat asymmetric thrust of the prop blade. However, by the time you got through with the offset thrust line, the fact that the shaft was angled, and the long keel/attached rudder configuration, handling under power in tight quarters became problematical.

With modern boats and the ability to "line bore" for prop shafts, there is really no reason to offset a prop.

Offset in reverse is a totally different issue. This is a function of prop torque due to running the prop backwards, further impacted by hull and fin relationships. You can mitigate this issue by using a feathering and reversing prop, like a Maxi (which looks the same to the water going ahead or astern). Steve

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I am thinking of changing my fixed three-bladed prop for something that causes less drag. The Autoprop from Brunton's Propellers seems very interesting. What do you know about it? P.S. Your Encyclopedia is a fantastic source of knowledge!

Hi Ulf: We have no direct experience with the Autprop. However, have heard mostly good things about them. The fact that the blades are twisted (rather than symmetrical as with a Max Prop) means they should be pretty efficient under power. There have been two complaints however. One is that these are somewhat noisy. Two, with a lot of motoring there tends to be bearing wear within the prop. If you go this route, let us know how it works out. Regards--Steve

A Reader adds:

Reading the comments on props--I can probably advise on the Autoprop, having had one of the early versions for 8 years, doing between 150-200 hours a season. It is far more efficient than the fixed 2-blader I had before that and has added nearly 20% to sailing speeds. It is also a lot more slippery than the 2-blade Gori before the fixed prop. Still water, under power, 7.2 knots on 29'8" LWL, boat weight about 7500 lbs, with a Yanmar 2GM20, about 1.3x displacement speed. The greatest positive point is being able to motorsail in light airs with the engine at 1/3 revs and getting 6 knots out of 5 knots true wind. Gasoil usage, overall, about 1.5 litre/hr. For the first time, this winter, I adjusted up the blade bearings, which were showing about 1.5-2.0mm play at the tips.

Disadvantages:

1. Noise when you first get into gear.
2. Accelerated cutlass bearing wear (it's a lot heavier than either the other two props).
3. Much higher anodic wear (the boss is aluminium-bronze, which makes for quite a couple) Until you're used to it--there's a delay before reverse starts to bite--the immediate reaction is to turn on more revs. Don't, you'll have the poor crew on the foredeck over the pulpit as the boat leaps backwards.

I'd certainly recommend any serious cruiser getting one--though in high-fouling areas you need to give a burst forward/reverse before casting off, to free-up the blades.

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What kind of prop do you use on BEOWULF and is it a feathering prop or folding? I know that you do motor sail and I wonder how you came to the size and pitch that you needed for the boat. I also liked the Bermuda story about the weather, you made a very good move by moving to a new location, it could have been a bad situation had you not moved. Good Sailing, Gary H

Hi Gary --just back from the Caribb. Props are a real cut and try situation-- but reducing prop speed and increasing diameter are a sure way to greater efficiency. BEOWULF has a Hundested controllable pitch prop. Very efficient, but also very draggy--Steve

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Steve... I have your Offshore Cruising Encyclopedia and I have almost finished building this 35' steel sail boat. I'm having a little trouble sizing the prop...Boat is 9.5 tons...engine is Farymann 32 HP...Prop is 16x13, 3 blade... Max. RPM under no load conditions is 2400. Max. RPM in forward is 2100 at max hull speed of 7.5 kn...reduction of transmission is 2:1. Should the max. R'sPM under load be closer to 2400?... Should top speed be reached before 2100?... I hope you can help with this ... Thanks--Basil

Hi Basil: You are asking a very tough question, with lots of variables.

First--there is a large section as you know in Offshore Cruising Encyc. regarding props and sizing. This will give you a pretty good start on the problem--it should get you into the ballpark (which is where you sound like you are at present).

The issue to look at is the max continuous speed (rpm) of the engine. With a fixed three blade prop, with twisted (and therefore airfoiled) blades, if you want to be able to use all the power in the engine, you need to be able to reach max continuous in smooth water.

The next issue is the speed length ratio at which the boat is operating. I am going to guess here and figure you have a 27 foot waterline. If you take the square root of this--which is 5.2, and then divide this into the 7.5 knots you are achieving you get a speed length ratio of 1.44-- which is very high (unless you have a very light, modern design, my guess is that your speedometer needs to be calibrated).

Most cruising under power is done at SLRs between 1.0 and 1.1 because mileage is better and noise and vibration are down. The normal top speed for moderate displacement boats is an SR of 1.3.

If you are now limited to 2100 rpm by prop size, it means the blade is a bit too big (on pitch or diameter--or both). This oversized prop will work efficiently at slower speeds with the bigger blade turning more slowly, as long as you remember not to overload (lug) the engine. Ideally, you should not run the engine at more than 75 to 80% of its usable power. So, if you max out at 2100 rpm now, you would want to operate at no more than 1680 rpm for long periods.

This will be OK in light airs, and when motorsailing--very efficient in fact. But when you are fighting headwinds and head seas, you may need more power. This is where the smaller prop comes into play. By allowing the engine to turn up to full speed, you have more continuous power available. But, at slower speeds and in more benign weather the smaller prop will be less efficient.

Just one of the many thousands of tradeoffs in sailboats! Regards--Steve

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Hi: Do you have a contact or web page for these products? Thanks in advance, John

Try 011 45 47 937117 in Denmark. Regards--Steve

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I very much enjoyed your Encyclopedias, Volumes 1 and 2...Do you have an address for the manufacturer of the Paul Luke "Hyde" propellers? I have used several Barrett and Maxiprops over the years, and have found them to be VERY inefficient compared to a fixed pitch (like 2.5 knots worth) It always seemed to me that a feathering prop with a little twist would be the answer, but I didn't know that they existed until I saw reference to it in your book. If it's not too much problem, do you also have a source for your "Murphy" gauges?

You can usually pick up Murphy gauges from large automotive stores. Also, they used to be carried by McMaster Carr in their catalog. Re: props, you are quite right about prop blade twist. Paul Luke's phone is 207-633-4971, and their web site is www.peluke.com. Also, you may want to check out the Autoprop, about which we've heard positive things.

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Steve-- In your book you seemed to like the max prop. Is this still your true? if not, what is your opinion on the Gori 3 blade prop?

Hi Dale: We tested one of the Gori props--I think it was a three blade version-- on the Sundeer 64. It seemed to work fine in forward, but not as well as the Maxi Prop in reverse. As we felt the maneuverability of the Maxi Prop was very important, we stayed with the them. That was about six or seven years ago, so Gori may have something new out. I suspect both would be good choices.--Steve

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Hi Dashews, Have 3 of your great books and getting a great deal from them. My yacht has a free-wheeling engine shaft and I understand someone has developed a system whereby you can mount an electrical generator inside the boat to the engine shaft via a belt and a set of pulleys--have you any information on this system, or contacts where it could be obtained? Regards, Mike

Hi Mike: You will find most of what we know about shaft generators in Offshore Cruising Encyclopedia. In short, what you need is an alternator which is wired for low rpm output--such as are used in deligery and emergency vehicles. Most alternator manufacturers make these.

Beyond this, it is a question of space--fit the biggest pulley you can squeeze in on the shaft and "overdrive" the alternator as much as possible.

Make sure that your gear box is happy turning without the engine being on (check with the mfg.), and be prepared for some noise from the rotating prop shaft. "Soft" mounting the alternator will also help with noise. Good Luck--Steve

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Hi, I've just finished your latest Storm Tactics, it's grate.I've also read and loved your others. Can you tell me how to tell if my prop is sized properly.I own and am planing on cruising my Rob Perry designed Islander 32. It has a Westerbeak 25 hrs . My engine manual doesn't say anything about max engine RPM. My current prop is a 12/14 two blade. At full throttel the RPM is 3400. I'm not sure what my hull speed should be,the waterline is 25', and I can't look it up in my Cruisers Encyclopedia because I lent it out and havent gotten it back.I can get .4 gal per hour and about 5kts at 1800 RPM. Is this too low of a power setting for long periods. Do deisel do better at higher settings. Is it hard on them to run at higher settings, say 3000 RPMs for extended periods.It seems that power settings above 2600 dont produce higher boat speeds.Any thaught on all the above would be a great help. Thanks

Hi Allan: You've posed a bunch of questions, and as we're leaving in the AM for Panama I don't have to time to give you the details--but I will try and point you in the correct direction. In the Offshore Cruising Ency. you will find the formula for both hull speed and power calcs. These are easy to run through and will give you an idea of the power required. The most critical part of this equation is the propeller efficiency which can be anywhere from 20% for a lot of two bladed sailing props to as high as 60% if you have something like our Hundested controllable pitch prop. Bob Perry can probably point you in the right direction on prop size/type, or your local prop shop will have some suggestions. As to what speed to run your engine, that is a function of how it is loaded, and what sort of design it is. Here I'd go to the local rep and talk to one of their mechanics. For example, you can run most 3600 rpm Yanmars at 3200 rpm for thousands of hours, and they are happier than if you run them slow and lightly loaded. Regards--Steve Dashew

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