transom rake

[almeyer]

I've noticed that a number of classic rowing small craft, for instance the Rangley and the Whitehall, have a small to moderate amount of rake in the transom. The Swampscott dory has what might be considered an extreme amount of rake. The Penobscot I built last year also has quite a bit of rake. Admittedly, the raked transom looks very sweet, but is there a functional reason for putting rake in a transom or is this just for looks? Just curious.
Al

[Thad]

It definately gives added reserve bouyancy aft, lifting the stern with the following sea for example.

[N. Scheuer]

It depends upon your point of view, Thad. One might argue that lengthening the waterline under a raked transom, thereby having more hull immersed aft, within the bounds described by the top of the transome, but of course putting the transome surface more vertical, actually creates more effective boyancy. I'm visualizing a wineglass transom, with fairly fine quarters underneath.

Moby Nick

[nedL]

Helps to keep you from being pooped so easilly. smile.gif

(That is when a following sea sloshes / splashes over the transom. At times, enough to sink you.) I do believe that the raked transom will help keep the backside of the person sitting in the stern-sheets drier.

[ 01-04-2005, 12:46 PM: Message edited by: nedL ]

[Nick C]

I've been wondering about the raked transom thing myself. I am building a dory a design I choose because you can mount the outboard, inboard. I like this idea because of experiencing a steep swell last year on my buddy's boat.

The swell was steep enough to occasionally slosh over the transom and into the boat. Since the boat was a Boston Whaler Montauk it really didn't have much of a transom or transom well, and this was more of a problem.

Just the same it seems counter intuitive to have a steeply raked transom on a dory designed for the Pacific Coast becauses they are often used for beach launches and landings. It seems a wave could chase you boat and dump that much more water over the transom while landing.

This all makes me wonder, how steep and how much of an angle can an ocean swell have? Now, combine this with the period between swells and what is a good angle and height for a particular length boat?

[Bruce Hooke]

Here's another factor to throw into the mix: take you typical dory and consider what shape the transom would have if you were to reduce the angle by moving the top of the transom forward, without changing the shape of the boat in any other way. The transom would get much wider at the top. Leaving other factors such as reserve bouyancy aside, that wider transom would not split following seas as well and so might be more likely to get "pooped". The underlying point here is that particularly in some types of designs, the overall shape of the boat may be an important factor in setting the rake of the transom.

Regarding reserve bouyancy, as I understand it the point is to have lots of extra bouyant volume above the waterline relative to the amount below the waterline in the same area. A raked transom achieves this, as does a wineglass transom, but a non-wineglass, non-raked transom does not. It is such a case that I think Thad was probably talking about. There are added benefits if the reserve bouyant volume is faily light so that it can lift quickly. Transoms are often heavier than planking so the wineglass solution would likely be heavier than a raked transom.

[Andrew S/Y Rocquette]

To quote Claud Worth:

"A long low counter of rather flat section is undoubedly dangerous in running before a sea, especially in a vessel of small freeboard. A counter of V-shaped section, in a yacht of good sheer and freeboard, may safely be made as long as may seem desirable. I have no experience of running before a heavy sea in a square-sterned boat with wide transome; but one would think that a large flat surface presented to an overtaking sea must be a source of danger. A small neat transome, well tucked up, is unobjectionable. Any type of stern may be perfectly seaworthy if of proper design. The choice will depend on one's idea of beauty, whether deck room is required for handling the after canvas, cost, and any special purpose for which the boat may be intended"

Source: Claud Worth, "Yacht Cruising", Fourth Edition, published by J.D. Potter (London, 1948) p. 293.

First edition was printed in 1910. Worth was talkig about small (10-40 ton) cruising yachts of the late 19th and early 20th centuries, but the comments apply to dory types as well, IMHO!

[Nick C]

In the case of the Dory you already have a lot of above the water bouyancy because of the sloping sides. Also, if you are building with the inboard well that opens to the back, you are losing some of the advantage that the sloping rear transom would give you.

Just the same, your transom height in terms of bouyancy is compromised by the cut out for your engine mount, although in the case of an inboard mount the rear transom would still have some effect.

As for the transom being wider if you eliminated the slope, you lost me there. No matter what you do with the transom the boat is going to be the same width at the rear. Unless you are talking about the old 'double ender'.