Ultimate SCUBA Boat?

[cid90]

Elaborate if you could sir. I want to learn as much as possible and do this thing right. It will be several years before my finances and certifications allow but TEACH ME MASTER.

 

[WreckWriter]

Originally posted by cid90
Elaborate if you could sir. I want to learn as much as possible and do this thing right. It will be several years before my finances and certifications allow but TEACH ME MASTER.

That answer your question? Gas is very explosive, diesel isn't.

Tom

 

[Marlinspike]

I agree with WreckWriter on the diesel issue as long as the boat is not below 27 feet in length. Otherwise it becomes an inefficient choice because of the weight and size of engines. Outboards are actually great in my opinion, for smaller boats.

Check out the Pursuit Denali 2670. It comes real close to being a perfect blend of large deck area, solid construction, and elegance.

http://www.pursuitboats.com

~marlinspike

 

[Rockhound]

Yup. They make diesel outboards. They are heavy and expensive, but I do recall seeing a couple.

However, a good inboard diesel, even in a 25' boat, will pay for itself in lower fuel costs, insurance and maintenance (actually, "breakdowns", since diesels do require frequent "diddling" to keep them running well).

Compared to gasoline engines, diesels are heavier, more susceptible to water contamination, costlier at first and a lot of people find the smell offensive. But, diesel fuel is more efficient (more btu per unit), less prone to accidental ignition (vapor) and generally easier on the internals of the motor. A diesel engine can last many, many hours before major work is needed (well, boats ALWAYS need work).

For a casual diver or a club, a nice gasoline outboard powered boat, preferrably one with twins for redundancy, is fine. For a professional dive op, diesel is the way to go....

Oh, and for the perfect dive boat? Mmmmm...a dream of mine, as well. A big cat would be nice, although the "flat" turns can be disconcerting. A catamaran designed for big water will ride more smoothly than a monohull of comparable length. Twin diesels would provide redundancy in case of breakdown, the wider beam would be more comfortable, as well. And, if I had my way (money!) the tanks would be extra large for those long runs offshore.

What else? I think a onboard compressor would pay for itself in reduced weight (one nice compressor is probably lighter than all the tanks for dives 2, 3, or 4 it would replace.). A nice cover over the main deck, or a even a full sunbrella enclosure would be a bonus, for those days when the weather turns nasty on the way home, or folks want to relax free of spray.

Setup? An aft mounted reel for a REALLY long trailing line, permanent mounts for a "bar" safety stop big enough for everyone to hang at exactly the same depth would be a bonus (with deeper lines below for deeper stops). Davits for a chase boat, maybe one with jet drive (SeaDoo), would be about perfect.

Oh, and an open transom for easy entry/egress.

As for hydrofoils...they are too finicky AND delicate. On small hydrofoils, weight and balance (as on an airplane) become critical. That's why some of the small sailing hydrofoils have center cockpits...to keep the crew in the center of the boat (although they seem to handle the heeling moment okay).

I would imagine that with too much weight aft ,the rear foils would dig in and slow the boat down. Too much forward and something else bad might happen (pitchpoling comes to mind). I have no idea how they would behave in rough seas...but I don't know a lot about them.....

Some of the bigger foils have adjustable angles of attack for the main foils, I think, which can address this sensitivity, but I wonder how much such a system would cost on a little dive boat.

Of course, a really big boat could employ SWATH technology, like that big liveaboard in the Bahamas. But that thing is indeed....BIG.

 

[Rockhound]

well, some of it. That Denali looks GOOD. I want one.


Tonight, I must buy a Lotto ticket.....

 

[Marlinspike]

As I recall, diesel outboards are more popular in parts of the world where the cost of gasoline is MUCH higher than in Florida. They make a sub-optimal choice for anywhere in the US.

~Marlinspike

 

[Marlinspike]

My ultimate dive boat would start off as a Jarret Bay 38 hull. For diving in North Carolina you simply cannot beat a hull with classic lines and huge flare on the bow. At 38 feet I think this size is an optimal combination of size, comfort, handling, and fuel efficiency. It would be powered by twin cat diesels. Then I would add a very large teak swim platform mounted low on the transom since it is much easier to just swim onto one of these than suffer needlessly on an aluminum ladder. Recessed into the gunwales would be the O2 kit and safety bottle for the 15ft hang line. The full compliment of electronics would definitely include the latest in weather, chart, and bottom displays. Side scan sonar would be nice too. Large fuel and water tanks would round out construction. A fresh water wash down on the deck would help rinse gear on overnight dive trips. Belowdecks, she would be finished in teak and navy upholstery with a full compliment of Riffe Spear guns stored where one might normally find fishing rods.

~Marlinspike

 

[WreckWriter]

I should have explained myself better. Outboards, regular gas outboards, are quite safe. Gas inboards are much less safe. The reason for this is that with an outboard the ignition source (your motor) is outside while the vapor source (your fuel tanks) are in an enclosed space (under your deck). If you put both sources in that enclosed space, a fuel leak can cause vapor buildup and when you add spark (like starting your engine), it can, and often does, explode. People die this way every year.

Gas inboards MUST have bilge blowers, explosion proof electric motor/fan units that clear vapors from the enclosed space BEFORE starting your engine. Any gas inboard (or I/O) without a blower (and a capt that knows when and how to use it), is a deathtrap.

I've never seen a diesel outboard but it somehow doesn't seem like a great idea.

If my "ultimate boat" had to be less than 30', I too would choose outboards. When I though of ultimate I kinda started thinking at about 55'

Tom

 

[Marlinspike]

I totally agree. I do not like inboard gas engines. Anyone who has ever opened an engine bay and smelled fuel knows what you are talking about. I was once on a modified donzi jumping swells when we smelled fuel. The hull had really taken a pounding and one of the fuel cells cracked. The bilge was full of 98 octane gasoline almost up to the dual battery mounts.

On any boat that is too big for outboards, diesel is the way to go.

~Marlinspike

 

[caymaniac]

I was thinking of someone who has already looked at that very idea. We were recently in the Turks and Caicos and dove with Fifi in Provo. I would say a downsizing of his boat would be a great start to the ultimate day boat idea.

Dive Safe,
Caymaniacut: