November 21 , 2005 - Too Short, Too Light, Too Tippy:
How to Stabilize a Yacht Tender
by Michel & Jane DeRidder

	Doing 20 knots in a once-tippy dinghy.

Not long ago we came across two different sets of friends who'd tried identical eight-foot aluminium dinghies to serve as yacht tenders. They were short and light and wonderfully easy to haul aboard, but they were dangerously unstable. These tinnies had upset and doused their occupants more than once. Michel decided - just for fun - to experiment with planing extension boards, as devised and tested half a century earlier, to see if such boards could convert short, light, tippy boats into something safe and usable.

He made a set of hinged boards out of 1/2" plywood, and attached them to the strengthened transom. The transom needed beefing up to take our 8hp Yamaha, as well as to provide support for the boards. The boards are 16" wide at the transom and taper down to one foot, three feet back. When extended, they are held in position by hinged aluminium tube legs. They extend the planing surface of the boat bottom, and can be folded upward out of the way when the boat is tied up or otherwise stowed. The boards are hinged with automotive type seatbelt straps fashioned so that by removing four screws each they can be taken off the transom with the wood strake that they hinge onto.

Then came the test run. Michel gingerly climbed in and lowered the boards, instantly gaining enough stability to be able to attach our 8hp Yamaha with a large inflated fender tied to it for good luck. With the added weight she became even more stable. After watching a short test run I dared to step aboard too. We'd put on life jackets, sealed the GPS into a ziplock bag, left wallets and phones behind, tied a long line onto the tinnie with a float on the other end...then laughed ourselves silly at high speed, a couple of septuagenarian hoons. That ultra-light boat, now remarkably stable, got up on its hind legs in seconds and flew! We sped along at 16 knots with two of us, and just short of 20 with just one. Last but not least, at rest the boards are in the water serving as efficient stabilisers.

With the 8hp outboard, that wee dinghy was a tad overpowered. Three to six horses would be a reasonable choice, or a pair of oars, but it is interesting to know what is possible, and it was satisfying to prove a point.

This absurd experiment shows that the board solution is a means of making a ridiculously Oh-Too-Short, dangerously capsizable dinghy usable. Just with a couple of plywood extensions on the transom, you can effectively fool a tiny vessel into believing it's capable of behaving like a longer heavier boat.

Boating Beginnings and Board Extensions

Our very first boat we conceived and built in the mid-fifties soon after we were married. We wanted a lot of boat on a limited budget. Not afraid to try something far out, Michel drew up a mini-sports boat that would ride on the back of our '41 Chevy. Nine and a half feet of fun and exploration, M'AS TU VU was equipped with windshield, canvas convertible top and powered by a 14hp Evinrude outboard in a motor well. Sitting on mounds of very necessary foam thickly covering the seat, we steered the speedy, pounding, gut-wrenching boat with a joystick, our feet straight in front of us in the covered bow. We could carry sleeping bags and air mattresses, a tent, a one-burner stove, food for a few days, and safety equipment of sorts.

	Level ride at low speed.
	Up on the plane.
	Stable at rest.

As short as she was, our plywood craft was extremely stable, but she was so short and heavy she couldn't get up on a plane easily. We had to encourage her by shifting our weight. Then came the oddball Eureka idea of extending her length using folding extension planing boards, thus fooling her into thinking she was longer than she really was. It worked a treat. She could now lift off onto a plane in a trice, and had even more stability than she had to begin with. When not on the plane, the boards ride under water and act as very effective stabilisers.

In our unorthodox craft we crossed the Gulf of Georgia more than once from Vancouver to the Canadian Gulf Islands. We visited various lakes in the greater Vancouver area, transporting the wee vessel standing up on the bumper of the '41 Chevy that we eventually sold for 50 bucks with 417,000 miles on the speedometer. We even ventured 100 miles up the Fraser River, then limped home, the outboard's cracked lower unit precariously wired together with a metal coat hanger tourniquet. Michel used that boat as his commuter, speeding to his work site in False Creek each day from our mooring on the Spanish Banks, leaving the Chevy for my daily commute to Burnaby. The trim-tab idea has since been used commercially, but the ones we've seen were never quite the same. (Too small and too short - they need power and speed to be of any use and they offer no stability advantage at low speed.)