twin or single

nitrox · 03 October 2010, 17:46

would you fit a single 300hp or twin 150hp engines on 8mtr rib. the boat is rock solid and weighs about 1600kg. what length leg do you require as transom is cut for 30". would 25" legs on twins fit neal

Screaming04 · 03 October 2010, 18:48

This is an endless debate.

A big single is far more fuel efficient, perhaps even faster (less drag)

The twins offer planing speeds with an engine failure.

I currently have twins and enjoy the security twin engines provide. (I do a 20 mile crossing of relatively unprotected water) I do wish I had the fuel burn of that single though...

My boat runs twin 25" shafts, it takes a 30" single, yours would probably be the same.

http://rib.net/forum/showthread.php?t=37459

martini · 03 October 2010, 19:33

Looking at where your boat is at in the build process I'd say you left it a bit late to ask this question!

How many fuel tanks have you got fitted? Many people inc. myself would suggest that there's no point in having twins if they're not rigged completely independant of each other.

Pikey Dave · 03 October 2010, 19:36

Ouch! This one's going to sting a bit. Firstly, performance wise a 300hp single will bury twin 150s. To get anywhere close to the performance of a single 300 you would be looking at least twin 175s possibly 2x200s. Bearing in mind you might need to run & plane on one. Fuel wise, twins generally use more than an equivalent single. But! I have found the difference marginal, I've found that powering boats in the upper end of the max rating & not flogging the engine(s) uses less fuel than running them at minimum hp & revving the knackers off 'em.

GordyP · 03 October 2010, 20:01

Agree with all of the above, the twins do make handling heavy load easier, if your going to have big groups of divers you may be glad of two props pushing you along.

Rogue Wave · 03 October 2010, 20:05

twins as per Martini's specs. the difference in performance at that level of power is just a bit of the top end the difference in Handling and control is massive

nitrox · 04 October 2010, 19:18

thanks for the info, single 300hp is the way. not sure which one, evinrude or suzuki cheers neal

Jonny2488 · 04 October 2010, 22:07

Quote:

Originally Posted by nitrox

thanks for the info, single 300hp is the way. not sure which one, evinrude or suzuki cheers neal

Suzuki all the way!! Absolutely no competition. I skipper a dive rib rigged with twin 200hp evinrudes and they simply aren't as reliable as I'd like them to be given the kinds of conditions I'm operating under and how important engine reliability is.

J