CAN A 24 RIB- RESCUE INFLATABLE BOAT RUN ON 2 90HP RIGHT ROTATION ONLY?
CANNOT FIND TWIN SET OF YAMAHA 90HP WITH OPPOSITE ROTATION HOW BAD WILL IT HANDLE WITH 2 90 HP SAME ROTATION
With great trepidation and utmost respect I must present an alternative point of view to Richard C.
I cannot talk on a hull fitted with two engines that is being driven right on the ragged edge over 50 knots – that sort of thing is pretty much off the radar for any normal rescue vessel as the general rescue conditions range from bad to horrendous in my experience. And the single over-riding principle in rescue is safety first – to get there, and return with no heroics at all given the frequently filthy conditions.
I have used twin engines on deep V hulls as a commercial operator. I never had counter rotating props, and while there is a difference in handling in a direct comparison there is not that much wrong with my set-ups over several thousand hours. If the trim tabs under the cavitation plate are set correctly and the boat is balanced well it went just fine with heavy commercial loads (if I was fishing right at least!) I use only hydraulic steering and never noticed any overt handling issues. And as a commercial operator I did experience storm conditions from time to time – it’s the nature of the game.
I currently command a 31 foot Noosa Cat Sea Rescue vessel with contra 250 yammies fitted. Frankly the steering is a little heavy at speed unless I pull the engines up and get the hull light but it certainly seems to go well in any weather I’ve taken her out in. Abalone divers tell me the hull does perform better with the contra legs fitted, but never so badly you cannot use it, more for economy and better punch out of the hole. (Another observation is that 500 hp (only got with premium fuel please note!) is not enough – another 200 would be enough to cruise with the full air cushion under the hulls while not revving the engines excessively, and that I am told transforms this hull into something else again. Dream on I guess….) I note the absence of trim fins on the big contra set-ups (replaced with a smooth plate), I assume this is due to the torque effects being cancelled out.
By the way, the fishing boat I am reminiscing on here used to get serious air when I was bored and heading out to the fishing grounds into the 2-3 metre gulf slop. It is a seriously strong work boat that flew real gentle and square, I used to get the props clear of the water for several metres at a time as if clearing the doubles on a motorcross track – no kick or twitch on landing and that’s with the throttles in one hand, the wheel in the other. I have no doubt contra props would improve the overall handling and economy – but there are too many boats on the water that go just fine with twins turning the props the same way to say that it cannot work. Having spent most of my time using same direction twins perhaps I have developed skills to handle them without thinking – I can’t say much on that although you do tend to work around handling issues commercially as you are often limited to what you’ve got.
If you fitted the engines you can get now and use the boat I am sure it will go all right, if you then swap a leg to give you the contra set-up it will be very interesting to know how you get on and if there is a massive improvement in performance and handling. Please let us know how you get on, the maker of the hull in question should have the greatest say in this – it is their design, and they should know if the contra props are an absolute necessity. If they are I’ll slink off back under my rock and look at pictures of my old boats and read my catch returns from 1999……….
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