Build

I'm building a new boat to withstand surf waves and hopefully stay upright and floating. The boat doesn't have to be super fast. I've built boats for flatwater, but need some advice on how best to keep things smooth with waves crashing.

I'm thinking a deep V hull design with deep and weighted keel?

Based on others I've built, it should weigh around 7-8 pounds, maybe more if I need to weigh the keel more.

I'm also looking for ideas for electric motor to power it.

Any good new designs people are using that might work well?

Thanks!

Ron Olson

My Feedback: (1)

You might want to look at the self-righting hulls in that size that use flood chambers. They're not that popular in the US yet but in Europe they have a lot of them.

Got RPM

A deep, weighted keel will cause more problems than it solves in turbulent waves. Ron's suggestion is a good one, but finding a 36" self-righting hull will be a challenge. You can modify a standard design to incorporate the flood chamber.

But I think that most of your design effort should be directed elsewhere. Using the boat in angry seawater means you will need to spend a lot of effort on sealing the hull - salt water and electronics don't mix at all. A hatch which seals reliably will be required. All through-hull holes will need to have fool-proof water seals. The flex cable will need to be sealed to prevent water from coming up the shaft. The interior surfaces of the boat will need to be completely sealed (if they are wood) so that you will be able to flood it with fresh water in the event that seawater enters. I think you get the idea - an upright boat with burned-out electronics is less fun than an inverted but undamaged boat.

For power you will need low speed acceleration to maneuver well in the waves. Consider a submerged drive. A hull that size can use 6S to 8S power to lower temps and extend run time. A 40x92mm motor with a Kv around 1000 rpm for 6S and 750 for 8S will allow you to swing a fairly large prop with reasonable run time.

You could run the boat on 4S but it will draw more amps and you will need the same weight of packs for the same run time. IME it can be better to use volts rather than amps for power: Volts x Amps = Watts.



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Build

Hi Ron and Got RPM,

Thanks for the great info. Flood chamber sounds like a good idea. I'm pretty good at sealing the hulls and have done some testing with crashing waves, but not one of my builds, just modifying other boats that were terrible with leaks.

I haven't really thought much about being able to flush the insides with freshwater, but that makes sense, thanks.

Low speed maneuvering through the waves also makes sense, but I'm still not sure which motor/prop, etc would work best. I'll probably test different setups and see which works best.

Do you think the deep v hull, no extended keel, with equivalent flood chamber would be the best choice for the hull?

Thanks much!

mfr02

The RNLI's self righting lifeboats usually rely on a large sealed superstructure for self righting. This causes a large light air bubble which combined with the heavy stuff being low in the hull, will cause an inverted hull to be very unstable, i.e., it will revert to being upright naturally.
Just a question of making the superstructure strong enough to live through a big wave lading on it.

Build

Mfr02,

I've seen video of the RNLI lifeboats in action and that's what I want. I don't get huge waves, but I have to run through a lot of 1-2 ft chop with stronger crashing waves behind them. I'm realizing I should build this to survive well while underwater and always right itself. I don't want to have to go chasing it.

mfr02

The old "Sloopy" FE had a flat section hull with the heavy stuff low and a large "cockpit canopy/fin" and was good at self righting if nobody had taped an electric torch to the top (entertaining evening session). I have recently watched a self righting cat racer do its thing after a flip - I got the feeling that the flood chamber worked well on flat water where that type of bat gets used most, I have doubts about its effectiveness on lumpy water.