I guess I won't be able to explain to you how a catamaran hull works.
One or two motors (split from 'Is there a valid reason for a pony bottle')
- Thread starter MichaelMc
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OP
MichaelMc
Working toward Cenotes
Catamaran hull physics is not really that complex. I do have some experience with small boats including: inshore racing skipper sailing quals, coxswain quals for a single hull 36' twin diesel, experience with a twin engine pontoon boat, and piloting in foul weather 50' vis into Chesapeake bay in a small twin engine craft.
If you lose one of your two engines you are not adrift powerless at sea. You have redundancy!!
If I'm diving manifolded doubles I have redundancy, but that doesn't make the second tank's purpose a redundant tank. You're trying to make two motors on a catamaran into a primary and "pony" motor. That's not how life works. A three stage rocket doesn't have two redundant engines. It needs all three.
OP
MichaelMc
Working toward Cenotes
I'll let the tech and cave divers comment on how manifold doubles are not for redundancy....
If one breaks you said you still make 10mph, but eat gas. You are still under power.
Ah... lighting all three would blow two of them up... Not much redundancy in space rocket engines....
OP
MichaelMc
Working toward Cenotes
If one of your engines dies, do you still have an engine that you can limp on?
Is your left arm redundant? Do you really need all four tires on your car? You can see and hear with one eye and one ear. This is nothing but ridiculous semantics. I don't drive the boat with one engine, keeping the other as a backup.
OP
MichaelMc
Working toward Cenotes
I mentioned that your boat engine redundancy is to a reduced, not full, capacity.
I dive sidemount, I use both tanks during the dive, while retaining some reserve in each. (Notice the parallel with "I use both engines to go/dive that far".) If I completely lose one tank, I still have the air in the other tank to breath, sort any issues out, and work my way calmly to the surface with safety stop, using my reduced air.
You have two engines which you use to push the boat at full speed. If one dies you still have one engine that can push the boat at reduced speed. The ability to push the boat is a handy thing to have. It beats the hell out of adrift powerless at sea. Yeah, the distance between your engines makes going straight suck. But it works better than no engine.
Yeah, ponies are typically not used at all unless needed for their redundant purpose. But there is no rule against an AL40 pony that I use some of as a stage, extra air, and keep some as a redundant reserve. This may be beyond the ability of your in need of more training friend. But pony is just one of the ways you can have redundant air. Its also the simplest to get started with.
This "I use both engines normally" does not remove the fact that having two gives you some redundancy.
I dive sidemount, I use both tanks during the dive, while retaining some reserve in each. (Notice the parallel with "I use both engines to go/dive that far".) If I completely lose one tank, I still have the air in the other tank to breath, sort any issues out, and work my way calmly to the surface with safety stop, using my reduced air.
You have two engines which you use to push the boat at full speed. If one dies you still have one engine that can push the boat at reduced speed. The ability to push the boat is a handy thing to have. It beats the hell out of adrift powerless at sea. Yeah, the distance between your engines makes going straight suck. But it works better than no engine.
Yeah, ponies are typically not used at all unless needed for their redundant purpose. But there is no rule against an AL40 pony that I use some of as a stage, extra air, and keep some as a redundant reserve. This may be beyond the ability of your in need of more training friend. But pony is just one of the ways you can have redundant air. Its also the simplest to get started with.
This "I use both engines normally" does not remove the fact that having two gives you some redundancy.
I didn't say it doesn't give some redundancy. It is designed to be used in concert with the other engine. It is not designed as a redundant engine. The purpose of a pony bottle is a fully redundant source of air. You shouldn't be breathing it as part of your bottom gas unless you need it. There is a difference between a redundant system and something that can be still be used if half the system fails. Each engine serves it's a purpose. I don't run one, then the other. I couldn't get the boat up on plane and would waste gas trying to use them as redundant engines.
johndiver999
Contributor
Wow when you can’t agree that a dual engine boat provides some degree of redundancy, we will never agree about diving
There is no way to power that hull from a single 300.
And in most cases dual outboards are less efficient (HP wise you have almost twice as much drag from the skeg) and end up failing together when they fail because fuel issue (water, bacteria, and/or sediment) take out both engines anyway. Sort of like bad gas taking out a set of doubles even if they are not synonymous.
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