M.B. Marsh Design offers a steadily growing range of plans for small watercraft. Our services include custom design, refit planning, condition surveys, failure analysis, systems integration and more.

Our designs hit what we think is an ideal balance between performance, capabilities, cost and ease of construction. Most of them are suitable for amateur or advanced amateur construction. These are boats that you can build in your garage, needing only patience, common tools, basic carpentry and fibreglass skills, and a willingness to learn. The resulting vessels are stylish, capable boats that will serve you well for many years.

From The Drawing Board

New designs from our drawing board, and assorted thoughts on boat design in general.

Outboard motorboat power calculations

Every year, mixed in with the usual chatter around the boatyards, I hear at least a few comments along the lines of "I beefed up the transom of my 14-footer so it can take 60 horsepower!"

Er, no. That's not how it works.

Maximum power ratings for small outboard vessels are calculated according to the size and design of the boat, taking into account the following factors:

  • Length of hull (longer = higher power rating)
  • Beam at transom (wider = higher rating)

Understanding monohull sailboat stability curves

One of the first questions people ask when they discover I mess around with boat designs is: "How do you know it will float?"

Well, making it float is just Archimedes' principle of buoyancy, which we all know about from elementary school: A floating boat displaces water equal to its own weight, and the water pushes upward on the boat with a force equal to its weight. What people usually mean when they ask "How do you know it will float" is really "How do you know it will float upright?"

Length matters

Longer boats are faster. We tend to take that for granted, because it tends to be true. Put two boats of similar type in a race, and the longer one is almost certain to beat the shorter one to the finish line. The difference that length makes is quite remarkable, but we rarely get to look at it on its own- and that is the subject of today's post.

Starwind 860: Range and efficiency

Among the key questions that must be answered in any powerboat's design phase are: How much power does it need, and how far can it go between gas docks?

The Starwind 860 trimaran that I'm currently working on started life as a series of computer simulations to answer these two questions. In today's post, I'll take you through some of these calculations and the logic that led to the final choices.


In The Shop

Dispatches from the shop: Progress reports on our boat building projects, plus some useful information for those of you who are building, restoring or repairing your own boats.

Boarding ladders for small boats

Getting into a boat from the water is HARD. The drag of the water makes it difficult to jump, and there's often no bottom to stand on. Even if you're in good physical condition, it's quite difficult to heave yourself more than about 15 to 30 cm (6" to 12") vertically out of the water. Take a look at a swimming pool: the copings are rarely more than 15 cm above the surface; in the best modern pools, they're level with it. Most people just can't jump any higher out of the water.

Let's look at Sunset Chaser for a moment:

Model testing the Almaguin, part 1: The framework

Computer simulations are pretty good these days, but there's still a lot they can't do. And as nice as it would be to have my own full-scale prototype of every boat I draw, that's just not feasible- there's never enough space or money for that. Models, though, are inexpensive, don't take up much room, and are fun to build- and, if done carefully with the right mathematical backing, can offer a lot of insight into how the full-size boat will perform.