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

1900kg for crew + divers + equipment

To be honest I think that needing to move something heavy will be such a rare event that it is not worth even thinking about at the moment - most of the vessels that we will be diving on will have been built at least 1000 years before anything heavy like cannons were invented. If we come across a need to carry something heavy then I think we will solve that problem when it occurs.

Absolutely - doing anything out here is difficult enough without going through the added complications of licencing a vessel over 12 metres.

Cruising speed of 24 knots seems optimum for the area, a maximum speed of 30 knots would suffice - any more would be a bonus but not really needed.

the 1200hp figure simply relates to 4x 300hp outboards after the coast guard dropped the clanger yesterday that outboards of more than 300hp were banned on all new builds - it was mainly relating to my thoughts that 2x 300 hp was not going to be enough, and obviously 3x 300hp wouldn't work that great on a cat. Am now going totally away from the idea of outboards though as 4x any size outboards sounds painful, so inboard diesels running props is the likely answer.

Do you mean like Kort Nozzles? Or props inside a long tube that is moulded into the hull?

 

I actually think that it might be time to start a new thread as things have evolved quite a bit since the thread started - certainly am no longer looking at a Stabicraft sort of vessel.

 

A well designed aluminium cat that is 12 metres long, with 2 x 300 hp O/B motors on the back should be able to achieve a reasonable service speed with a reasonable complement of divers on board.
The 15 metre ally cat in my avatar photo has 2 x 150 hp O/B motors, and when they were fitted she did 25 knots flat out with about 10 people on board.
When she was built 22 years ago she only had a pair of 70 hp O/B motors, but she still managed a top speed of about 16 knots then with 10 people on board.

 

Have you considered Z drives? They are ideal for maneuvering or staying in place.

 

Trouble is, you have a few threads 'on the go' already - I think it would be better to just have one thread for everything, in similar fashion to what @DogCavalry did with the building thread for his Sea Sled -
Sea Sled madness. It’s in my brain. https://www.boatdesign.net/threads/sea-sled-madness-it%E2%80%99s-in-my-brain.63079/

Yes, this is what I had in mind - although nozzles will probably knock some knots off your top end speed.
Water jets would probably be better for your purpose if you have inboard engines - but they are very expensive relatively.

 

If a 12 x 5.5 metre Polson cat with the big forefoots(forefeet?) to compensate for the very forward cabin will cruise at 24 knots using twin 300 hp with 1900 kgs load of divers + kit etc then that is definitely the way to go. Obviously that isn't my field of expertise but I just didn't think that twin 300's would be enough, but if so then happy days and problem solved as that will also give us DPS etc using Yamaha's Helm master system.

 

I haven't - but just looking at them on Wikipedia I get the feeling that they would be similar in price to jet drives?

 

Seek and ye shall find:

Lorne Campbell Design : Sea Sled Dive Tender http://www.lornecampbelldesign.com/boat-commercial-military-SeaSled.htm
Complete with interesting comments.

And:
https://www.thehulltruth.com/boating-forum/889308-project-sea-sled.html

 

A lot of threads have fallen by the wayside as the feedback from here has caused them to be discarded and aren't relevant any more. Now that I'm settled on a hull design(er) - Poleson I think that things will be easier from now on. I will start a new thread on the Poleson and stick to that.

I agree that waterjets would be better if we have inboard engines but one of the problems that I've faced is that there is basically no information on the net on what waterjets cost - there are plenty of sites where you can lookup the price of outboards or inboards, but finding a price for waterjets on the internet - any water jet is just about impossible.

 

new thread is Poleson Marine diving vessel https://www.boatdesign.net/threads/poleson-marine-diving-vessel.67627/

 

Unlike jet drives, they rotate 360 degrees.

 

You better check with Mr. Poleson. I've only seen 70hp engines on those boats. If the 12m uses a bigger engine, 150?

The hull design is key and it may not tolerate 300hp per hull..

 

I'm just going to put my broken record back on. Sea sled. Better in every catrgyyou care to name. Except low speed cruising - that flat bottom makes surface drag.

 

One of his youtube videos shows the MV Temptress with twin 225 hp Hondas.

 

How can you talk about the power of outboards or intraboards or waterjets, or whatever, without even knowing the shapes of the boat? This is all turning out to be quite absurd.
First you should define the type of hull, draw a body lines plan, then calculate the hydrostatics, estimate the weights, study the stability under given loading conditions and, when all that is done, check the necessary power.