Introducing a Fuel Efficient Power Trimaran
Russell Brown (from ptwatercraft.com) recently told me about a fuel efficient motor powered trimaran in his neck of the woods. He thought this would be a very interesting boat for many small trimaran enthusiasts.
He was right!
Russell then introduced me to Brandon Davis, the owner and operator of Turn Point Design, a unique shop in Port Townsend, Washington that specializes in fabricating parts for watercraft. Brandon has 20 years experience in the marine trades and has created the fascinating power trimaran you’re about to see here for one of his clients.
Brandon’s business specializes in creating 3d computer cutting of tooling, molds and parts for composite applications. He has produced custom parts for some very sophisticated boats over the last three years, including 100+ parts and tools for racers in the America’s Cup.
With this in mind, I asked Brandon if he could share a little about this very unique trimaran. And he generously shares some great info with us here (many thanks Brandon :-) The renderings and photos below are courtesy of BOTH Brandon Davis and Russell Brown)!
A Fuel-Efficient Motor Powered Trimaran in Port Townsend
by Brandon Davis
First boat was a Hobie 14. Been crazy about multihulls since. I spent 7 years as an international fisheries observer– glorified fish accountant. Mostly worked in the Bearing Sea, Gulf of Alaska, West Coast of the US, and Southern Indian Ocean.
My wife and I started/ran a charter sailing/kayak business in the San Juans for 5 years. The boat was a Cross 50 trimaran (Pelican – now Moxie) with kayaks on top– we offered 3 and 5 day sailing mothership tours aboard. That was a very tough business– got out of that and started a small CNC cutting business in the San Juan Islands.
In 2006 I started cutting parts and molds/tooling for BMW/Oracle– first for the AC32 monohulls and after that for the AC33 trimaran. I am heading to NZ shortly to work on the new AC45 catamarans being built by BMW/Oracle racing (Core Builders).
The idea of a better power boat really came when operating a couple small power boats professionally in the San Juans. Both these power boats (Aluminum workboat with a 120 hp 4-stroke & Safe Boat with twin 50 hp four strokes) were considered very fuel efficient but only obtained 3 miles per gallon on the water on a good day— cruising at 20 knots.
They were also extremely uncomfortable with large chop. I thought there had to be a better way. Then I went for a ride on Russell Brown’s power catamaran. It had a very comfortable ride and sipped fuel. I was hooked on the idea of building the ultimate efficient power boat.
This trimaran was a collaboration between myself and its owner — Nigel Oswald. He is a moth sailor and wanted an efficient powerboat to get around in the islands with his family. We brainstormed quite a bit, read as much as we could about Nigel Iren’s Voyager and the Earthrace trimaran … and consulted quite a bit with Russell Brown on his experiences with similar craft.
The goal was to make a power boat that was as efficient cruising at 20+ knots as possible. It must be able to operate comfortably in small chop … whereas many planning boats of this size become very uncomfortable.
The boat would be for transporting people on the water from point A to B as efficiently as possible — not a weekend toy — but a boat to transport people in most any kind of weather quickly and efficiently.
The boat is 24-feet long but only weighs 250 lbs (500 lbs with motor, fuel, and all other bits). We were pretty sure that we could get to 20 knots with a narrow displacement hull shape and 20 hp if the hulls were slender enough and we kept the weight down — from Russell’s experiences.
The foils are designed to take the boat past 30 knots and allow it to cruise very economically at 22 knots. They are designed with a movable top bearing so that the angle of attack of the foils can be changed while under way to adjust for speed and sea state.
Ideally, they will lift 80% of the boat weight and allow the main hull to ride on a flat planning surface on the main hull. It would be impossible without the foils, to make such a long narrow surface plane (unless you throw way too much hp at it). The goal is to have this flat surface control the pitch of the boat, which will also ultimately control the angle of attack of the main foils.
The boat is designed to carry 3 adults or 2 adults plus two children. There is a provision for turning the seats into a berth, or taking them out and turning the whole cockpit into a long storage area/ pickup truck bed.
The lifting hydrofoils have not been installed on the boat yet … but without them the boat is able to cruise at 20 knots with a 20 hp motor. It should do 30+ knots with the foils. But it was also important to us that the boat could perform well without foils.
It took my shop about 3 months of work (spread out over 8 months) to complete the prototype. The hydrofoils and foil trunks are installed, but we still need to put the windscreen on and install the bearings for the hydrofoils when time and money are available. We have learned quite a bit so far with the prototype and hope to make some later changes to refine the boat.