Need help on catamaran model!

[depthofit]

Very true. When i started planning this i had completely no foundation at all. I came from a marine engineering course and i always had interest in boat design and so for my final year project i decided to give it a try.

Initially, i planned my boat to be driven in enclosed freshwaters like reservoirs, with waves not an issue in reservoirs, i would have less factors to be concerned with. Next i realise that i would want stability and load carrying at primary concern, so i went with hard chined boats which has the most volume and thus less draft, less wetted area and less drag. Tell me if i said anything wrong. The project dateline is on friday and there is not enough time to build a new and correct one, any remedy?

What state should my model be in to be considered capsize? Or in another words at which point should the range of stability of the model end.
Can i still continue with the test where i load weights along CG and measure to heel? Or does it really has no meaning at all.

[Calculator]

Stick with what you have, considering the deadline. Capsize should be when it completely rolls over. I doubt that this can occur in the actual boat unless you attempt a really high speed turn. Then your flat bottom and hard chine may cause it to trip and roll over, especially with your elevated cockpit. The only way you could get a static capsize is for you and several of your friends to stand on one hull, hold onto the cockpit and lean back. You can calculate how many friends you need to submerge the hull.

[depthofit]

Anybody know how i can calculate the total resistance of a real size boat if i have the total resistance of its model at 1:20 ratio.

I understand that if i were to propose a suitable horsepower, i would need to know some kind of information regarding efficiency of the outrigger and everything. Do anybody know roughly the coefficient of efficiency for them?

[depthofit]

What is the problem?

One of the values we gathered from the towing test was at 1.85m/s, our boat experienced a 3.5N drag. Using this piece of information, i attempt to break down the 3.5N into frictional and residuary resistance using Rf = FSV^n for frictional, subtracting it from 3.5N would yield residuary.

For residuary resistance, i believe i could use

Residuary of actual boat/Residuary of model = (length of boat/length of model)^3

During towing, my model's displacement would be 330g(weight of the model without anything) + 480g(weight of loaded weights) at a draft of 3cm, the wetted surface area was 818cm^2. I then estimated the WSA of the actual size boat to be the square of the boat: model ratio which is 20:1.

Ultimately, using FSV^n (actual boat) + (Residuary resistance model x 20^3) sheould give me a close estimate of what the actual size boat resistance would be.However, the frictional resistance i calculat
ed for the model is too small to be true.

L=length of boat=0.54m
P=density of water=1000kg/m^3
F = (P/1000)(0.1392 + (0.2581/2.68+L))

Rf = FSV^n
= 0.219 x 0.0818 x 1.85^1.825
=0.055N

0.055 is way to small...

[martinworswick]

not sure if i can say this but try asking your questions at boatdesign.net-a lot of knowledgeable folks in their, alot of designers also.

sorry mods if i can't post that link

[Talbot]

I noticed an earlier comment that waves were not being considered as it was a reservoir. Some of the worst sea conditions for a small vessel I have experienced were on a lake. The seas can get very steep and with a short periodicity. Even if conditions are benign, wake from other vessels can cause significant wave issues. These can get compounded by reflections from the shore especially where the shore is a cliff edge.