Re: Howto lengthen a hull by inserting a parallel midship section in DELFTship?

[Peter Edmonds]

I’m VERY new to DELFTship, and very much welcome that DELFTship can address the real world of cut and spread vessel lengthening. I throw in some observations from my most recent lengthening experience.

The subject vessel was 14 m aluminium, monohedron with 2 diesel jet units. She was cut around the engine room forward bulkhead, and a complete new compartment, 7 x 600 mm frame spaces was added. This was primarily to increase passenger numbers through more deck space. we put new fuel tanks in the new space to keep fuel LCG suitably aft.

The boat has suffered a deteriorating performance as outfit weight was progressively added ost-completion. It was alleviated to a small extent by extending the bottom aft of the transom with non-buoyant planing boards. The loading on the planing surface was quite high. (I use Taylor Model Basin Series 62 data).

The increased length gave a small increase in lightship (and thus loaded) mass, but a substantial increase in planing area. This generated a small increase in top speed, but a big gain in performance at “cruising” power; say 70% of full rpm.

I hope this is of value and encouragement.

Peter Edmonds, Perth, Western Australia