another single vs twin thread: performance

[the man]

So, this thread is NOT about the OPINION of having two outboards vs one. It IS about the objective (if that exists) info on weight, power, speed, fuel consumption, etc.

I live in a place where I cross straits (juan de fuca) that can get ugly in a hurry- a kicker is not what I want when the breeze is coming up, it is getting dark, and I have to work the next day. So "right or wrong" the decision is made- I want twins for redundancy. I will also have two alternator/battery systems and a stand-by fuel tank that I fill separately.

There are probably threads on this already- but I could not find any.

The boat I am looking at doing this with now is very light- it has an 85hp Suzuki two stroke now and goes 40kts. What if I put two 60s on it? What will be the difference in actual power compared to re-powering with a 115? (yes, boat is rated for it). I know 2 will weigh more, cost more, more drag, etc. But I have no idea- will the two 60hp be the same as having a 115hp on there as far as speed & fuel economy, etc- or better or worse?

Also, how can I figure out if this will plane with one engine? (and the other one lifted) Is there a way to figure this out without actually doing it and then finding out it doesn't work?

Note: I am thinking Etecs. As far as weight, two 60s = 480 lbs. A 115 plus 15 hp kicker = 505 lbs. Twins, in this case, are lighter. Or- is there something I do not know here?

Thanks in advance

 

[magnumdeke]

Re: another single vs twin thread: performance

What is the rated hp capacity and type of vessel? I have Twin 50's on a 18' tin hull, it will not plane out on one, it will maintain plane if I get it up on two. Fuel consumption is at least third more or so on the twins than one, Also one engine of comparable hp would give a better top speed based on less drag. My rebuild I am doing for big water will have a 150 and a 15 on it. if you are worried about engine failure maybe you could go with a larger kicker, say a 20 to 35 hp? Go for highest horse with the least weight?
Just my two cents, should be better ideas out there.

 

[CaptainKickback]

Re: another single vs twin thread: performance

my $.02

You said things can get ugly real fast. I assume your interest in top speed is so you can beat the storm back. If a couple of knots makes a difference as to whether you beat the storm or not, then I'd say you going to get caught in some of the storms. Once things get ugly, top speed is out the window unless you want to beat your boat and passengers to death. Also, if one engine fails, even if it won't plane, you still have a much stronger kicker than you would with a primary/kicker setup.

You will give up significant fuel economy running two engines.

Sorry, can't help as to one 60 hp getting you on plane.

Sea ya...

 

[Texasmark]

Re: another single vs twin thread: performance

Part of the getting on plane answer is that you have to ensure that the lower unit of the unused engine is completely out of the water.

Gut feeling, if you can run 40 knots with a pair of 85's you ought to be able to run around 35 knots with a pair of 60's you certainly ought to be able to get on plane and once there run adequately on one engine. If you need trim tabs to achieve that then so be it.

Tell you what. Answer your own question. Take your current rig out with one engine kicked all the way up. Can you get it to plane? If so, how well. Do a little extrapolation for the 60's you mentioned and you should have your answer.

Mark

 

[ondarvr]

Re: another single vs twin thread: performance

Gut feeling, if you can run 40 knots with a pair of 85's you ought to be able to run around 35 knots with a pair of 60's you certainly ought to be able to get on plane and once there run adequately on one engine.

Mark

He has a single 85 on it now.

 

[ondarvr]

Re: another single vs twin thread: performance

Also, how can I figure out if this will plane with one engine? (and the other one lifted) Is there a way to figure this out without actually doing it and then finding out it doesn't work?

Thanks in advance

How can an answer be given when the only information supplied about the boat is that it is "light".

 

[jimmbo]

Re: another single vs twin thread: performance

Here is an old test but should still be relevent today

 

[Texasmark]

Re: another single vs twin thread: performance

Here is an old test but should still be relevent today

Very interesting test data and by a reputable source. I too am surprised at speed and fuel consumption. On weight, I just figured reduced drag caused the increase, not the addition of transom weight and I still feel that's the answer.

Thanks for posting.

Sooooo are you going to go with your twins?

Mark