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Old 07 January 2015, 15:20   #1
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Opinions Please

Hi All
I am looking to power the 5.5m chinook I recently bought with only a small budget.
I can't decide on either twin 2 stroke 40s or a single 2 stroke 75.
Is the twin option going to be much more expensive to run ?
and is there a certain position they have to be in ?
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Old 07 January 2015, 15:31   #2
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The old twins vs single engine debacle! Do a search on RIBnet, there's literally hours of reading material on this subject.

Regardless of budget, everything is more expensive with twins. You have added weight at stern, increased fuel, servicing costs, and rigging, if you include separate fuel filters which is essential.

For my money a 75hp engine is without question the best option. With the money you'll save, stick an auxilliary engine on for back-up.
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Old 07 January 2015, 15:34   #3
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100 per cent agreement with Spartacus. Regards Jim
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Old 07 January 2015, 15:45   #4
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Twins have their place in the world, but you'd need a special reason to choose twin 40s on a smallish boat.
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Old 07 January 2015, 16:12   #5
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Twins have their place in the world, but you'd need a special reason to choose twin 40s on a smallish boat.
Just because they look cool

But really I have the mind that if one should break down I have the benefit of the other as opposed to only having a small aux without the power to get me anywhere fast.
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Old 07 January 2015, 17:39   #6
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Just because they look cool

But really I have the mind that if one should break down I have the benefit of the other as opposed to only having a small aux without the power to get me anywhere fast.
To actually get this benefit you need 2 totally different electrical and fuel systems. Carefully selected with just this purpose in mind one 40 HP will get you home - but badly planned it will have the wrong prop and struggle.

If you use your boat in situations where twins makes sense and the cost and performance disadvantages etc are outweighed then you probably wouldn't be asking.
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Old 07 January 2015, 18:36   #7
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Separate fuel and elec No problem
Carefully selected prop will be trial and error I guess.
The situations I plan on putting this boat into are more adventurous than I have been in the past.
I want to do a trip to the scilly isles and if that goes well a channel crossing.
I have gone further in distance but always hugged the coast.

The twin idea is like a crotch, it is supposed to make me feel safer.
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Old 07 January 2015, 19:12   #8
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The twin idea is like a crotch,
aye its certainly not far away

Quote:
it is supposed to make me feel safer.
Look up "risk compensation"

if you want it - do it - but its not the approach 90% of people here would take. Service engines well, know how to trouble shoot and fix minor/common issues, keep a close eye on performance indicators / warnings, a decent sized aux, cruising in company, investing in better comms kit. Having 2 engines is no certainty that you won't run into a problem.

Whilst I wouldn't want to be stranded mid channel you are actually in an area with (1) lots of shipping (2) pretty reasonable comms (3) good rescue coverage - and in a 5.5m boat you presumably would only be attempting it in pretty good conditions.

If the boat has not been rigged for twins before you may have some work to do - and it may not be trivial (e.g. involving irreversible angle grinding!).
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Old 08 January 2015, 10:59   #9
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" Risk compensation is a theory which suggests that people typically adjust their behavior in response to the perceived level of risk, becoming more careful where they sense greater risk and less careful if they feel more protected. Although usually small in comparison to the fundamental benefits of safety interventions, it may result in a lower net benefit than expected. "

That is so true.

Well serviced and in the best condition I can get them.
Being a mechanic the troubleshooting and fixing is no problem along as I have the right tools at hand, i.e Duct tape,wd40 and cable ties.
Crossing in company would be great but I have no friends with boats.

I think its probably not the worst place to be stranded but trying to make head way with a little aux is not the way I want to go, and yes I only plan on crossing on the finest of days.

Maybe I should be looking for a decent size aux that has enough power to push me along at decent rate but at the same time be light enough not to hamper performance.
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Old 08 January 2015, 12:26   #10
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Bear in mind that this is coming from a bloke with a twin engine boat (for sale) & who has a single engine boat on order:-


Twin engine, I specced this as a dive boat, the rationale being that we were diving 20+ miles off shore, deep stuff. If I put divers in the water, I wanted to be sure that I could get them out again, especially if they've been drifting a couple of hours doing deco. The boat has completely separate fuel & electrical systems for each engine, it will plane on one engine, the fuel tanks can be combined to a) run both engines from 1 tank, or b) 1 engine from both tanks. This means that the loss of 1 engine or 1 fuel tank doesn't mean you lose the corresponding engine/fuel. Similarly, the batteries can be combined to run/start/charge from any engine.
I've even gone as far as having separate plotters/gps so that failure of one unit doesn't mean the loss of the whole system, paranoid moi???


New boat:- Single engine, smaller boat. I've stopped diving & now don't need anywhere the level of redundancy. We still do the distances, but usually in company. We are well equipped with drysuits/plb/290N lifejackets yada yada! If it all goes brown, the worst that happens is we drift/anchor & wait for the cavalry.


Twins are undoubtedly more expensive to buy/own/keep. In your case twin 40s will nowhere perform as well as a single 75 of similar pedigree. Unless you have under deck tanks, you will have fuel cans all over the place gobbling up valuable deck space.


At the end of the day, it's your call. You did ask
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