Will it plane?

[F3M4]

I'm attempting to design a catamaran used for inshore fishing. I'm pretty sure i've got the right idea, but wanted to double check with some more knowledgeable people. The boat will be a center console with an outboard motor powering it. The boat length will be roughly 16ft long and 7.5ft wide.

[Richard Woods]

Most flat bottomed vessels will plane with enough power

So I think the real question to ask is "Will it plane efficiently"

Answer probably no

I think you don't have enough buoyancy aft and by implication also have too much rocker. Also your hulls seem quite wide, or put it another way, your boat seems heavy

Have you seen my Skoota 20 powercat design?? Seen on my website. Maybe something like what you are planning

Richard Woods of Woods Designs

www.sailingcatamarans.com

[F3M4]

Richard, I have looked at your skoota design, but unfortunately it doesn't quite fit my bill.

I am hoping to be able to reach higher speeds, as the areas in which we will be fishing require a fairly long run. The cabin design also doesn't afford much usability to the fishing aspect.


I gathered from your post that the hulls would benefit from being more slender. I am wondering how much this will affect my draft.....

I don't need a ridiculously low draft, but it certainly would be beneficial to my fishing efforts.


I will revise my "design" and post another version up.

[Doug Lord]

One thing you could do, besides studying Richards excellent work, is to look closely at existing power cats that meet your requirements-maybe Glacier Bay
or other similar boats might provide you with a starting point. You would, in all likelyhood, save money in the long run by engaging someone like Richard Woods or another experienced power multihull designer to put together a design specifically tailored to your requirements.

[F3M4]

The glacier bay 2265 is nearly exactly what I am looking for. My only concerns are the draft(17") and the length is a bit more than I want. I also want to stick to one outboard.

In the end I may certainly wind up working with someone like Richard, but I am a stubborn engineering student with the tools and free time to attempt my hand at designing the vessel.

I'm going up to 20' in length, as I see no reason not to. I'm also going to forfeit my low draft in lieu of more speed/wave handling.

[F3M4]

Here's what I've come up with, it's amusing how different from my first attempt these are.




Should I incorporate a small flat part to the bottom?

And I forgot to thank you guys for the advice. I really appreciate it.

[PAR]

I would strongly recommend you buy a set of plans. The questions you raise suggest you haven't the necessary grasp, in the fundamentals of yacht design. At least not enough to develop up this cat. This isn't a personal dig at you, just an observation based on your drawings and questions thus far.

[F3M4]

I mean, I understand the concern, but the problem is that I can't find any appealing plans that suit my needs....

No one has designs for a power cat around the 20' range that fits my description.

Unless, of course, I'm missing them?

[Frosty]

I think your design could be improved on.

To me they remind me of a frog in an ice cube.

sorry --I could'nt resist it

[DaveJ]

Schionning have plans for a 6.5m powercat that i think meet your requirements.

http://www.schionningdesigns.com.au/...udyPlansa4.pdf

[F3M4]

Originally Posted by DaveJ

Schionning have plans for a 6.5m powercat that i think meet your requirements.

http://www.schionningdesigns.com.au/...udyPlansa4.pdf

This is close, but way above budget....
Thanks for the link though.

[F3M4]

Originally Posted by Frosty

I think your design could be improved on.

To me they remind me of a frog in an ice cube.

sorry --I could'nt resist it

The name frosty must be describing your heart

[Spiv]

I owned several power cats of different sizes and shapes, so what I discovered might be of help:

• cut the drag by having nearly flat transoms, just a little V is OK.
• transom trailing edge to be sharp (to loose the wave and get planing)
• don't have any rocker, actually planing boats might even benefit by sinking the transom a bit (just the last metre and just a little, this will help keep the bows down and help the ride).
• keep your stems vertical
• have a wave-breaker in the tunnel and no flat surfaces, the Mantacat was the best cat I had. Se picture of a Mantacat tunnel.
• have asymmetric chines (planing strakes) so the boat will react gently when hitting waves. What I mean is the outer and inner chines should be staggered.
• you will need an XXL outboard shaft, I suggest a Yamaha. You might have to design a little pod in the middle of your tunnel so that the cavitation plate is just below water when planing, but check that you don't drown the engine when not planing.

Hope it helps.

[Doug Lord]

Originally Posted by Spiv

I owned several power cats of different sizes and shapes, so what I discovered might be of help:

• cut the drag by having nearly flat transoms, just a little V is OK.
• transom trailing edge to be sharp (to loose the wave and get planing)
• don't have any rocker, actually planing boats might even benefit by sinking the transom a bit (just the last metre and just a little, this will help keep the bows down and help the ride).
• keep your stems vertical
• have a wave-breaker in the tunnel and no flat surfaces, the Mantacat was the best cat I had. Se picture of a Mantacat tunnel.
• have asymmetric chines (planing strakes) so the boat will react gently when hitting waves. What I mean is the outer and inner chines should be staggered.
• you will need an XXL outboard shaft, I suggest a Yamaha. You might have to design a little pod in the middle of your tunnel so that the cavitation plate is just below water when planing, but check that you don't drown the engine when not planing.

Hope it helps.

----------------
Very interesting info, Stefano-thanks! I'm wondering why the asymmetrical planing strakes seem to make a difference. Did you try them symmetrical first or were they studied by the original designer? Intriguing....

[F3M4]

Originally Posted by Spiv

I owned several power cats of different sizes and shapes, so what I discovered might be of help:

• cut the drag by having nearly flat transoms, just a little V is OK.
• transom trailing edge to be sharp (to loose the wave and get planing)
• don't have any rocker, actually planing boats might even benefit by sinking the transom a bit (just the last metre and just a little, this will help keep the bows down and help the ride).
• keep your stems vertical
• have a wave-breaker in the tunnel and no flat surfaces, the Mantacat was the best cat I had. Se picture of a Mantacat tunnel.
• have asymmetric chines (planing strakes) so the boat will react gently when hitting waves. What I mean is the outer and inner chines should be staggered.
• you will need an XXL outboard shaft, I suggest a Yamaha. You might have to design a little pod in the middle of your tunnel so that the cavitation plate is just below water when planing, but check that you don't drown the engine when not planing.

Hope it helps.

Thank you, this is exactly what I'm looking for.