Help, Delftship calculations

[Roland Stockham]

Hi all
Newbie on Delftship and struggling with the calculations tab. I have a hull model with no leaks, finally!! When I put in the numbers - 1.25in wall thickness and 25lbs/cuft for western red cedar plus one layer of epoxy glass - the weight it gives is nonsense, I think it was around 27 ton for a 35ft hull. All the other stats do make sense but the weight estimate is one of the main ones I wanted to get, plus balance.
Also I cannot find whether the estimated weight is supposed to include machinery, tanks etc. Is this a light ship weight or just a hull weight. I am assuming the factor value, default 1, is the scaling for machinery but does setting it to 1.000 mean it adds nothing or assumes hull weight is 50% of light ship weight?
Thanks, Roland, Voya 11 project

 

[bajansailor]

Re the lines plan that you have in Delftship, what value does it give you for the displacement (disregarding any wall thickness for the hull)?
And what is the draft when Delftship is claiming that your displacement is 27 tonnes?

Can you post a copy of your design on here for reference please?

 

[Roland Stockham]

Been away working for a few days but here are the requested figures.
These are the hydrostatic calculations I get and a copy of the project. The aim was to develop ideas from the Folkboat and see what happens if you change three parameters - reducing to forefoot so she lies hove to pointing higher and to stop the tendency of the bow to easily blow off, increase the free-board both for a drier boat and better accommodation and reduce the transom rake to increase the waterline length compared to overall length. Does this improve the design as a cruising boat or kill it? As you will see it is giving me weight of 48.7 tons and a displacement of around 12.5 ton with a hull construction weight set at 25lbs per cubic ft. This suggest not only that she would sink but gives a W/L length : displacement ratio in the 400's, I would want that to be around 275! Clearly I have done something wrong.
PS I have tried playing with some settings and think that one error is that the turn of the bilge is too slack. If she where about the right weight (around 8-8.5t) she would only have a draft of 4.25 which looks all wrong. To get to a sensible weight I had to reduce the hull construction weight to 4.25lbs which is impossible.

 

[Roland Stockham]

Nonsensical weight problem SOLVED, there is a bug in my version of delft ship, if you change to metric it all works out!! Now I seam to have the basics I have bee redrawing the design and it is working out much better. Also having solved the weight issue I can balance displacement and weight. Will update the project plan shortly when I have finished tweaking it

 

[Roland Stockham]

Nonsensical weight problem SOLVED, there is a bug in my version of delft ship, if you change to metric it all works out!! Now I seam to have the basics I have bee redrawing the design and it is working out much better. Also having solved the weight issue I can balance displacement and weight. Will update the project plan shortly when I have finished tweaking it

This is the 'tweaked' version and looks like it is a feasible project. Using composite construction allows a lighter stronger hull and removes the restrictions on radious of turns around the bilges (the original Folkboats had issues with cracking frames). This allows the keel to be extended forward and the internal volume to be increased without making here much to heavy. Running the numbers with 70sq/m of sail and 3500kg ballast gives 9.3 ton displacement with a displacement length ratio of 324, SA/D ratio 16, ballast ratio of 37% and a 'motion comfort of 41. The goal is for a very traditional heavy displacement boat for extended expeditions in remote area of the Canadian/Alaskan coast with the emphasis on comfort and easy single handing rather than speed. She will have a generous auxiliary power system in the motor/sailor range and a short bowsprit to carry a large goaster. The rig will be a ketch with about 60% ratio between main and mizzen. She will also need substantial tankage which was the other reason for raising the cabin sole. I checked the weight calculation and it is right, hull skin comes in under 2 ton! By the time you add deck, superstructure and bulkheads etc aim would be to be in the 4-5 ton range which still leaves more than a ton for machinery and equipment. In any case load carrying capacity is around 50cm/ton. Would be interested in what you think