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.

Inboard or outboard?

An important decision in any powerboat project is the choice of exactly what powertrain to use. Our Starwind 860 is now almost at the point where that decision must be locked in.

Should it be an inboard or an outboard? Gasoline or diesel? What kind of propeller?

And, importantly, why?

Risk mitigation philosophies from the radiation world

Quite a few issues of safety, in the yachting world, come down to the preferences of the skipper and crew. There will never be universal agreement on how (or if) to use tethers, or on where a life raft should be kept, or on whether an extra EPIRB is a better investment than an AIS-B transponder upgrade.

We can, however, apply some general principles of risk analysis and risk mitigation at the design stage. The maritime world already has some ways of figuring this out, but for today, I think I'll shake things up a bit with some principles from a different field: ionizing radiation.

Starwind 860 design logic

"Why that?"

It has to be among the most common questions I get about the Starwind 860 trimaran. Why a tri-hull? Why that size? Why is it a powerboat?

Here's the short version of the design logic.

Dynamic Stability of a Monohull in a Beam Sea

The last post in our series on yacht stability looked at the static case. We saw that a yacht's response to heeling forces can be described by a stability curve, the shape of which tells us a lot about the boat's purpose, sailing characteristics and seaworthiness.

A real yacht in a real situation is of course far from being a static case. The static stability curve is one of our best tools for quantitatively comparing different designs, and I don't mean to denigrate its importance. In practice, though, dynamic factors can often have a bigger effect on the actual stability of the boat as it relates to safety, seaworthiness and comfort.

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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.

Crossbeams, little by little

Trimarans are finicky to build. There really aren't too many ways to simplify the highly loaded crossbeam structure, particularly when (as in our case) it has to be able to fold for trailering.

Our Starwind 860's aft crossbeams are now sitting partially assembled in the garage. The webs, the strut blocks and the centre blocks are in place, and it is now time to start closing them up.

More S860 crossbeams: Centre bearing blocks

The Starwind 860 trimaran's crossbeams are joined on the boat's centreline by a massive hinge pin. This mechanism ensures that the two outriggers fold in sync. The peak load on the centre bearing could be up to 41 kN (about four tons) port-starboard or 11 kN up-down, and the structures around it need to reflect that.