by Jeff Gilbert

Gumboots Update

The Original

Plans are afoot to commence building the fast cruising, open decked 31 foot Catamaran Gumboots in Australia in 2005. This sis the one from which building plans will be derived. Hulls are around 31 x 5 feet.

The triangle bottom shape in the drawing below (with 10.5 WL length to WL beam) may never be developed to build plan stage despite my belief that it will outperform any boat hitherto designed upwind. Weight is thrown onto the lee chines, which are angled 3 degrees upwind. These hulls automatically fight lee drift. The triangle footprint makes builders nervous for the wrong reasons, the boat has been shaped & balanced not to bow plunge, but the inevitable losses are in the exit waterflow which is not as clean as a conventional hull.

The new bottom is still a dory, but faster at better than 12 to one. It makes the main cabins bigger and the aft Head and Navigation cabins are a little longer and narrower in footspace only. You can still seat 4 in opposing pairs for cards, but two of the seats are fold downs and the big comfy 2 seater with room to stretch legs right out is the go.

click to enlarge

Transportable Version with New Bottom

Interest in a version of Gumboots that could be transported in a container led to a concept redesign, involving a more conventional bottom shape to enable a narrower overall hull. Take away the 5-foot beam & the accoms are a problem, eased by redesigning the bottom.

Some containers are as narrow as 91 inches. The space can be eased by putting the hulls nose past nose, with centrelines offset a foot over the container length. With packing they cross 12 feet aft of the bow where the hull is 94.3 percent of its beam.

The hulls I’ve sketched here are 4 footers and will go in a container 91 inches or 2300mm wide. Just. No room at all left. Unless one can find a bigger container for sure the hulls should be on 3.75ft frames, or else one may face paying for two.

A packed up 28-footer crosses at 83 percent of its beam and so can be much wider.

The safe options for guaranteeing container ability:

  • 28 x 4.25 interior beam
    (8540 x 1300 on a 700 sole/bottom)
  • 31.17 x 3.75 interior beam
    (9500 x 1145 on a 600 bottom)

I’ve sketched “Gumboots Alfresco” below to try and show what sort of space is available in a 4-foot hull.

The 31 hulls packed simply cross too close to their point of maximum beam to get good hull width. Put up with it or double the work with deck level accommodations.

In many ways I’ve drawn the wrong boat here, a 28 with wider hull beam would be the best way to go. Not as fast as the 31, the 28 may as well make the sole wider and get very comfortable. It could thus be comfy enough without deck pods. The missing meter would come out ford of the crash bulkhead, the cockpits and the dining table, a bit everywhere and you wouldn’t miss it much except in miles made good.

The “Galley” hull has an athwartships galley with the corner of the bench stepped on to get below. The sink is off to one side; its structure supports the dagger case or outboard dagger rungs at bridgedeck level. A stronger method would be an extra box beam from dagger case to case.

The narrower hull has angles which means very comfortable fold up seats can be created facing outboard with an athwartships seat of 30 inch width in which 2 might jam if they were in love. Otherwise it’s a great armchair. You wont be playing bridge without the 5-foot wide hull. The ford berth is 84 x 34“ too tight for two.

The “Owner’s Stateroom” hull would have the berth in the wider part of the hull and high, losing a bit of potential cabin space to get about a 43 inch wide double in the 28 foot version, and a 39 incher in the 31. Still leaving enough room for a thru shower entry, and good dressing space. The drawing is in one-foot squares, print it and have a scribble. There’s room for a deck accessed single forrd. Some may prefer to raise the cockpit and put a single berth each end of a large open space.

Over the 31 x 5 hulls in a previous article, you lose nothing but the width to stretch. Gumboots is a small yacht, really best for 3 on a trip, but very safe offshore with thru bridgedeck draining, high clearance, deep cockpits and extreme stability.

I’m not saying it’s easy to build. I am saying it is possible for a human to do without wrecking their life, where most offshore designs are not.

If you wish to move your Gumboots, it must be built in its simplest form so it’s demountable. You could build independent deck pods containing double berths that lash on the deck slats, and take them with you.

Gumboots Alfresco

A homebuilder’s Dreamboat, buildable from the bare and simple transportable model. You might do this after sailing the basic Gumboots for many years, or accidentally having a family! I know it’s pretty basic, but to my way of thinking it’s a massive job and this is why the boat can be built in stages. Note that this could be done to pretty well any cat with 20 feet of beam. If she were 28-footer, the bridgedeck eatery or a berth would go, as you couldn’t carry the beam comfortably.

Having transported Gumboots where you want to be, you will probably want more room. Gumboots Alfresco is a two-stage idea involving putting doubles berths up on the bridgedeck.

click to enlarge

The mast would be raised a foot as shown to cover the pod, but if you added the screen it would go up a further 18 inches. The windspeed to raise a hull at 29 knots on the beam is so high that this simply isn’t an issue – the beam of the cat makes it extraordinarily stable and she’s a very swift reacher as a result. The screen covers a really nice central dining area that seats five, which is about the most you’d take on the boat. Inside there is space to seat 4 or 5 around a table for dining or a game of cards, but both outward facing seats and table fold down in halves with a cutout bulkhead, a necessary evil, between them. You wouldn’t sit in for a long period, as unlike the other larger seats you can’t stretch your legs out. The aft armchair provides bracing for the cook at stove, sink or chopping board.

On deck there is a substantial centre beam to build as a footwell; it could also take motor and fuel. If you were sure to go this way you would already have built it in the original.

The biggest plus is the spray protection afforded the bridgedeck on this fast boat. Others are the apparent room inside, giving a massive increase in resale value.

The biggest minus is your boat is no longer demountable, and that this is a massive job, taking nearly as long as the original build.

How fast does it go?

This is as useful a question as “What colours does it come in? But I’ll try.

In a swift cat you invariably wind up on a reach as you pull the apparent wind onto your beam. On a good day, reaching in the basic 2 ton no-frills clear decked 31 foot Gumboots with the sail plan drawn, you would be cruising along happily with a 21 knot wind off the beam and the full sail plan up, alert for gusts, and your sails developing 25 horsepower. You have a power to weight ratio of 200 lbs per HP and you would in a conventional mono be travelling at speed to length of 1.85 if the hull could manage it. These hulls can not only manage that, but also have a fineness factor on their side, which will boost the S/L to 2.

I’d expect the boat to be cruising calmly at 11 knots.

The top end is fairly wide open and depends on skill, nerves and sea state. If you have a strong steady 25-knot wind and flat sea 15 knots plus is possible. Many claimed 20-knot boats will overturn before Gumboots, which, sailed correctly, will sideslip if she lifts a hull, and won’t capsize at all. By this I mean if you are trying to reach in gusty, lumpy conditions you should pull up the lee dagger board and point a little more upwind. If a hull flicks up you will simply sideslip and drop back in.

Heavier Gumboots will be slower in light airs and relatively faster than a stripped light version in heavy going.

Richard Boehmer’s respected “Base Speed” formula predicts seaway passagemaking in 24 hours as follows:

  • 28 foot container Boots loaded to 5000 lbs @ 181nm/day
  • 31 foot open deck Boots loaded to 5600 lbs @ 206 nm/day
  • 31 footer stripped to 4400lb (say a race?) … @ 232 nm/day

Immersion is around 660 lb an inch and you can take a ton of junk to sea.

Literally. But it will cost you 15 percent, 30 nm per day, or 1.25 knots.

Final Comments

The one to be built, Jim Townsend’s, is the best of Gumboots as it follows the creed of absolute simplicity. It will be slightly modified to a more conventional bottom giving an improved aft run, a bit more speed and improved accommodation space. No need of bridgedeck accommodation. The new bottom allows the main beam to move forward up to 2 feet – I tried this to its full extreme in the drawing above which has slightly longer cockpits as a result. The final position will be determined by a weights study but will probably be at 10 feet to the old eleven (and the above nine). Moving this beam gives a bigger cabin and more overall space especially over the berths. With the new bottom and the five-foot hull beam they can be 42 inches wide not 39, sited right where designed below. The five-foot hull beam does allow better damping and the boat will be plenty fast, and incredibly stable, able to run with full sail in a force five. This is largely due to the low tack and wide beam, and roachy fully battened main. I’ve just designed an almost identical sail for a 30 foot Simpson Little Bear, which will be a good indicator. With Little Bear at 4 tons, the same sail will certainly move this 2-ton ship, which is wider and lower in CE, and will handle it with ease but very speedy results. The main drawn this time around is both slightly bigger and slightly lower in centre of effort.
You wont need any more than these two sails and a storm jib.

The main beam is the hardest part of the build in the demountable form. Were the boat not demountable there would be much merit in simply building a sweep of accommodation across the boat, boxing this monocoque structure front and rear into infra-beams.

Of course this still has to hold up the mast, meaning more infrastructure.

We will see what happens when Jim, myself and a few other champing at the bit Gumboots builders give the boat our full attention next year.

Jeff Gilbert - 2004