A boat from yesterday for tomorrow

What the world needs is a truly economical planing-hull power boat. I'm the designer of Tolman skiffs, built of stitch-and-glue plywood, which are economical compared to other boats in their class due to their relative light weight, but the sad fact is an 18-wheeler running down the highway fully loaded gets better mileage than I can get in my 22 x 8-foot Jumbo skiff. A diesel engine would doubtless make it more efficient, but diesels are not commonly made as outboards, and the usual ways to install them are as outdrives (inboard/outboards), which are very expensive to buy and to maintain, or with conventional straight shaft-and-rudders, which result in boats that are deep draft and difficult to trailer because of a keel or other appendages. Neither drive system appeals to me.

Enter the Seabright skiff. This traditional boat was developed by many different builders for fishermen along the New Jersey shore that had to launch over beach due to the scarcity of harbors in the early 1900s. These skiffs used conventional inboard engines (gas in those days) with straight shafts and rudders, but what made them special was that the prop, running in a tunnel, which along with the rudder was placed entirely above the bottom of the hull. Thus these skiffs drew no more water than the hull itself, which because of its flat bottom, was often only inches. The peculiar shape of the stern, with its pod-shaped underbody and cut-away transom, gave these boats a good turn of speed, several times that of displacement-type boats of equal power (think sailboats), yet they were more efficient than conventional planing hulls (like Tolman skiffs, for example).

Perhaps the most famous modern version of a Seabright skiff was made by Robb White of Thomasville, Georgia, for use in the shallow waters of the Florida Panhandle about five years ago (see his article in WoodenBoat Magazine, March/April 2006). His so-called Rescue Minor (the name refers to a Seabright skiff designed by naval architect William Atkin in 1942) draws only 6 inches and powered with an 18 hp Kubota diesel achieves more than 20 mph and 20 mpg. (It should be pointed out each of these numbers drops to less than 20 when the skiff is loaded with more than just the operator.) Although the design plays a large role in his skiff's super efficiency, doubtless its extremely light weight also is an important factor. Robb built his skiff like a strip-built canoe out of poplar wood cut on his own land. Furthermore, his skiff had very low sides, saving more weight. His engine installation employed a belt-drive system derived from a garden tiller which he built himself that eliminated the conventional clutch and reverse gear, yet a further weight saving.

You would have to judge Robb's effort an extremely successful boat, but the freeboard while adequate for his needs is too low in for most of us to feel comfortable in. Furthermore, his act is a hard one to follow for those of us who want to buy our mechanical parts off the shelf and want to build in plywood. Still, it gave me an idea.

What I have done is to take the traditional Seabright skiff underbody and graft it on, so to speak, to my Standard Tolman skiff design to give it more freeboard and interior volume. In the process I lengthened the Standard skiff from 20 to 22 feet but diminished the beam from 7 to 6 - 6 to reflect the proportions of traditional Seabright skiffs, which were relatively long and slender. In the process I think I have improved the bow by eliminating the hard knuckle of the original Seabright skiffs, which tends to make such boats yaw (bow steer) in a following sea. In other words, the bow looks much like that of a typical Tolman skiff, and we know these handle well. The bottom is flat, not veed, and although I have railed against flat bottoms in the past, the Seabright skiff has a feature which is said to mitigate pounding. The aft end of the tunnel has a slight downward curve, which deflects the water coming from the prop with the effect of forcing the bow down. Thus the hull punches through the seas, rather than rising over them and slamming down. (Robb White verified that this principle works.) This bow-down aspect can generate spray, but I have included the usual double sets of spray rails that are so effective on the Standard Tolman skiff.

Twenty to 25 hp engines are appropriate for this skiff. I intend to power my prototype with a 20 hp Yanmar diesel with a conventional clutch and reversing gear. I bought a used engine and gear, but I had to buy a new gear which has a 1:1 ratio rather than using the stock 2:1 reduction gear, which is designed to push displacement hulls. The Seabright tunnel permits only a small diameter prop, which must be run fast to get planing performance. This is an off-the-shelf item, however, and not too expensive. I expect to cruise at 17 mph. Economy will be outstanding as this engine burns 5/8 gph at about 1,900 rpms.

A diesel setup like mine if new is about double the cost of an outboard of comparable power and thus has a long payback given the amount of hours the average boater drives per year. There may be other choices. Diesels made in China are significantly cheaper. To my knowledge these are not yet marinized, but it's perfectly possible to do this, as Robb White did with his Kubota, or have it done. (Basically, the exhaust manifold must be liquid cooled.) Air-cooled gas engines are cheap although noisy. Diesel or gas automotive engines are a possibility. Making a belt drive system like Robb's would also save money and weight.

It might even be possible to run a Seabright with an outboard in a well, although there is a problem with this. When the skiff is at rest, the water pickup ports on the engine are above the waterline. My solution would be to mount the engine on what is known as a jack plate, a stock item used on bass boats. This fits between the engine and the transom and operates electric/hydraulically to raise and lower the engine. (This is a wonderful feature on any shallow water skiff, by the way.) You would lower the engine 4 inches or so starting off to immerse the water intakes, then raise the engine as you get under way and the tunnel fills. In the running position the lower unit of the outboard (and here I'm thinking of a 25 hp Honda) is completely shielded by the hull, and since in this position the ventilation plate on the outboard would be snug against the roof of the tunnel, you would steer with a separate rudder, the same as with an inboard installation.

I think fuel savings alone aren't necessarily the Seabright/Tolman's biggest advantage. There's a lot of thin water in Alaska tide flats and rivers, and a skiff that draws only 6 or 7 inches with full protection for the prop has a tremendous attraction for a hunter and fisherman like me. And as a lot of boaters know, there's a lot of other places on earth with shallow water, as well. So maybe the Seabright skiff's time has come again.

Plans for the Tolman/Seabright are available in the form of a 25-page pamphlet (eleven sheets of drawings, which include directions for installing an inboard engine and building the rudder). This is to be used along with my book Tolman Alaskan Skiffs since construction of most of the T/S is similar to my Standard Tolman skiff. The price is $30 plus $5 for Priority Mail ($10 for Global Priority to areas outside the US). My book, which includes plans for three skiff designs, is described on my Web site.

Renn Tolman - www.alaska.net/~tolmanskiffs
Alaska, June 2007

This book contains very detailed plans for how to build all three of my skiff hulls and the information necessary for adding many options such as decks, storage lockers, steering consoles, and a variety of cabins. The book is 8 1/2 x 11 inches in size and has 250 pages. There are 175 drawings and over 100 photos.
The book and CNC cut kits are available from Skiffkits in Alaska. The book is also available from Duckworks.
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