Would anyone like to design a 39 foot/12 metre Stabicraft-style boat?

fallguy are you able to help me a little more by explaining your comment? Are you referring to longitudinal centre of gravity with the weight of the outboards at the stern offsetting the weight of the cabin being so far forward? Or something else entirely?

 

Well, catamarans are generally more weight sensitive than monohulls, but even monohulls without a deep forefoot would suffer from a very forward pilothouse.

And the Poleson catamaran has one very forward pilothouse, so I really wanted to see the forefoot.

And the forefoot is basically like a big massive bow extension which explains quite a bit about how the vessel is able to stay level with all the weight up front.

If the hulls did not have the big forefoot; they would plow and the boat would not trim well except when planing.

As it is the boat just seem to plow a bit through the water in the video.

The boat would serve your purpose well, but might be a little more fuel hungry than a boat with the house back more and less forefoot. But for a dive vessel; the ga is really great. Lotsa room in the cockpit for divers gear and to ready. I think the only thing to verify is top speed and then you probably want to run jet drives as another poster advised.

Not sure how you would dps with props and divers down; sounds like a bad recipe if the aft cockpit is where divers come to the boat.

 

Cheers DC - I emailed him yesterday, hopefully might get a reply today/tonight.

 

He's just posted another build on his facebook page - Poleson Marine LTD https://www.facebook.com/polesonmarine - unfortunately I can't make out what size the outboards are, but the speed figures look good. If you scroll down to his post on the 18th of October you can see a good photo of it out of the water.

Many thanks for your very detailed reply - that really helps as I can have a basic understanding (I think) of how CofG affects a boat on flat water but lack the understanding of behaviour in seas etc.

Fuel hungry here is not quite as bad as it would be in other countries - 95 octane is about US$1.60 per U.S. Gallon, diesel is about $1.15 per gallon.

I really like the GA, as you said for a dive boat it is really great - for here add an awning that covers the entire back deck, then add s9me bench seats with tank racks behind them like this

The DPS is mainly for one particular site, the diver lifts will be placed just aft of the pilothouse on each side of the boat so probably 20-25 feet away from the props, and the descent/ascent line will be dropped from the bow so the divers should be well clear of the props, and will paint the underside of the hull around the props in very bright danger stripping to warn them to keep clear! This particular dive site will be in 65/210 feet so the divers doing that dive will be very experienced divers.

But jets would be nice! One of the problems with jets though is getting an idea of the pricing - with google its very easy to find pricing for outboards, pretty easy to find pricing for diesel inboards like Yanmars etc, but but prices for jets seem to be a deeply hidden secret!

 

That lift is inadequate for rough weather. Even in 2 foot waves (60cm) it would be really dangerous for a diver to get in. A ladder with steps open on the sides would be much safer for the divers when the boat is pitching.

 

I would hope we can get a more detailed and experienced reply from one of the NAs. Mine is somewhat amateurish. A large forefoot may also slam in heavy seas, but with the weight forward, I'm guessing she'd have a certainly decent speed in head seas still. A good designer ought to be able to tell you directly how the boat runs and is to be run in 6' head seas as well, so I'd ask him.

 

I just realized you are an engineer/diver. That is what I do too. Unless you are doing live boat diving the propeller are not an issue. On smaller boats, when live boating, we always turn off the engine when divers are surfacing and getting on the ladder

 

Just retired, was a FHWA-qualified underwater bridge inspector. The diver lift and props are going to be one of those things that I think we will write the procedures once we get to see it all - will be a little bit to work out!

 

If any of the naval architects can jump in that would be appreciated!

 

@RSD, I'd be happy to take a closer look at what you already have and what you need from an NA. Send me, if it seems appropriate, a pm with the information you consider necessary.

 

I meant to assess the effect of the wide forefoot on the Poleson boats.

 

I missed a few details in your SOR, @RSD . Dave Gerr and a sea sled is still the way to go, but the interdictor isn't as ideal as imagined. A new design using that as a starting point would be better.

 

I haven't received any reply from Dave Gerr, but I'm in touch with Tommy Poleson and I think that is the way that I am going to go - his design with the cabin far forward leaving tons of deck space ticks a lot of boxes.

 

I do like those Tommy Poleson designs - they are very neat.
However take note that they are designed to be load carriers - they have to be able to carry a fair amount of deadweight / cargo.
The deadweight capacity of your boat will be much less probably (just divers and equipment? Or lots of recovered treasure as well? ) hence you should be able to make your hulls a bit skinnier, which should give you a bit less drag?

 

Good advice to dial it in; too much extra capacity would not be ideal.