View Full Version : Displacement for 27 foot fast cruiser

Henning 4148
11-27-2005, 08:27 AM
Imagine a 27 feeter. Basically for harbour hopping / fast and save cruising for two for approx. a week, max. sleeping four. Slim, with a length / beam ratio of 3,5 on deck and approx 4 on the waterline to make her go to windward. She'll heel a bit and may be a bit wet but should have nicer movements in a seaway than many modern boats. Construction should be epoxy strip plank on laminated frames or ply stitch and glue on laminated frames. No standing headroom below.

Now, imagine the boat without the deadwood and keel. What displacement on this boat without fin would be sensible if you want a seaworthy vessel?

If you want it to be a moderate long keeler that can stand alongside the harbour wall, would you opt for the classic deadwood / ballast (the deadwood has some significant volume and therefore adds some significant displacement to the hull shape), or would you go for a thinish steel plate with balast bomb (thus adding very little volume and displacement to the pure hull)?

Reason for asking - when noodling hull shapes for the above fast cruiser I seem to end up with something like 2,7 tons of displacement for the hull without fin. Now, with a classic deadwood this would throw me in the ballpark of 3,5 tons overall displacement. To be a fast cruiser, this again would ask for something like 40 sqm of sail area which is quite a lot for 8 metres LOD (ok, sail areas like that have been known on classic racers of that size and a displacement of 3,5 tons on this length was not out of the way in days gone bye, but ... ).

The ways around this seem to be either to replace the deadwood with a steel plate which has much less volume or to reduce the volume of the "hull without fin" or both.

Any recommendations which ways are preferable for the above design brief (fast seaworthy cruiser for two for 1 weeks passages?).

Any recommendations which displacement to aim for for the hull without fin?

[ 11-27-2005, 08:30 AM: Message edited by: Henning 4148 ]

11-27-2005, 09:32 AM
Alden design #337 is a centerboard Marconi sloop, 25' x 20'7" x 7'6" x 15". It would be interesting to know what her displacement is and how ballast was configured. Herreshoff design #473 ELFRIDA from 1896 has 21'6" wl x 8'b x 9"d, a centerboard boat with lead probably outside -- it would be interesting to know her displacement and lead configuration (with that shallow draft!). John G. Alden Co. in Boston for the first, kurt@mit.edu at the MIT Museum for the second.

11-27-2005, 06:46 PM
I would say that you are way too heavy Henning, I'd think about One metric tonne at most.