6m powercat

i use fgi r 180 resin 304$ for 20l and really like this as for the curves coming to the front of the boa ill do these with 2 sheets of 3mm ply bend one and laminate the second over the top of them, then ill butt block them to the rest of the outer hull

bugger strip planking!!!

i think it would be possible to bend the 6mm but easier but slower with 2 3s, as for my angle coming up for the bows i am still tossing up whether to run the hulls full width to the last metre(not as pretty) but like you say better for bouyancy or start them at the 4.5m mark to get a nicer curve

the first layer of epoxy will literally dissapear into the wood the second and third seal it off, you need to add glass to give it strength the epoxy adds minimal strength without the glass but seals the ply nicely

sean

 

add a foil to the tunnel

Have you thought to add a foil to your tunnel Sean?

 

yes and no i have just been loonking into this but i have no idea how to go about it, ill probably build it first and then think about whether it needs it later

im still just wondering whether i can just build a boat using commonsense without using some sort of planning software and even whether im on the right track, i have an educated idea that the motor will do the job but am not sure whether my hull chines will be to steep( more power needed to get on the plane but better ride in the rough), whether my bdeck is to low ?? and at what draft it will float at , how far to extend the first 25 degree chine etc etc
this is why i posted to this forum in th hope that some of the gurus may be able to help, otherwise ill just build it and see what happens
sean

 

I did it with little effort to my 19 ft sciff and it is perfect http://www.buildboats.info/sportfishingmcatamaran.html

I'll be happy to share it with you Sean

 

I used oak 1x2 laminated and then wraped in glass was pretty basic stuff really

 

did you give it a profile ie naca 12? did you v it and support it by the tunnel, did you put little foils on the back and if so where do you place them is there a formula related to boat length or did you just guess, did you give it an angle of attack?

thanks for any and all assistance
sean

 

out of curiousity if i wanted to tiller steer your boat would i be able to see over the bow? is there any way to have a foiled boat with a more bow down attitude,
i only ask because my preference is for tiller steered boats due to the quick response you get in steering, when you are hooning around over reef sometimes you have to make lightning quick decsions to avoid a bommy sticking out?
plus i also want fairly high sides on my boat which would compound the problem even more so
sean

 

I gave the foil 2 degress of incidence against the line of the keel and I developed my own shape since I wanted a foil to generate lift between 10kts and 15 kts, so it would plane fast. I chose low sides for fishing and I had liitle money so it took less material to build that way. I am adding more to the topsides. I haven't added aft trim tabs yet as The engine has a dolphin I made, that works well. I am adding move able tabs this spring to help with weight changes due to passengers moving around. I built the boat 15ft long first then cut it in half and added 4 more ft.. you know its never big enough. If your running around corelheads... I'd think about adding nylon runners to the hull bottoms like a airboat use, then all you need to worry about is the prop. The foil runs right at the surface so that should be fine and yes you could use a tiller. I used a V foil with a strut in the tunnel. I would go strait next time. You could a kevlar to the bottom also.

 

if you have a straight foil do you still reckon youd need a strut in the middle for support?
when you say you developed your own shape, does this mean that their is an accepted profile for foils on cats or that you chose foil that would give you large amounts of lift at low speeds(with the resultant small amount of drag at high speeds)
sean

 

also if you place rear foils should these be placed right at the rear of the boat ? also how high up the hull should these be mounted at the bottom so that you are trying to get the most out of the foils lift to get maximum hull out of the water or slightly up from the bottom
sean

 

It depends on how wide the tunnel is and how thin the foil you build is. I have herd that winglets help to reduce vortex generated by symetric hulls. I have tried this yet buy will be this summer. Trim tabs should go low as possible.

 

is a winglet like a rear foil or is that a trim tab, also sorry about the more questions than answers approach i just like to understand something before i do it

sean

 

out of curiousity to simplify hull design can you just take a set of hull frames from a boat like the fao boats and split them down the middle to create your assymetric hulls or is there a little more to it, i have drawn up a set of plans but a friend suggested this approach to gain a bit of an inside track in terms of design, the fao boats have the beam that i desire to use when halved for my hulls width plus they look a little funkier than what i drew up. are there any major problems with this approach?
sean

 

any input?

 

If they are around the dimensions you could always use the plans as a basis for looking at number of bulkheads, stringers etc anyway.

But can't see why not, effectively that is what an assymetric cat is.