Anyone had twin four-stroke outboards?

Nick_H

Nick_H

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www.ybw-boatsforsale.com
We viewed and sea trialled a boat in Greece yesterday, fitted with twin Suzuki DF140, 2008 year but fitted new in 2010, 500 hours, good service history.

They started easily and purred nicely at tick over, and once warm they ran smoothly and reached max rpm under load, with no smoke.

However, at low to mid RPM under load, whilst warming the engine, they sounded quite rough. After a few minutes like this, as RPM increased, there was a noticeable point at which the noise changed and the engines became much smoother, and we could then reduce rpm without the noise coming back.

I should have picked up on it at the time, rather than just making a note to discuss later, as the boat is now out of the water and i'm back in a different country. However, by chance we did capture some of it on video: http://s171.photobucket.com/user/ni...p4.html?&_suid=138997236725809554969741803709

From about 12 secs onwards you can hear a noise that sounds a bit like a steam train in the distance. It did get worse after the video finished as the revs increased, then as I say, suddenly went smooth.

Is this just down to the engines being out of sync? It seems a lot of noise just to be caused by that, but i've never had a twin outboard boat so I dont know for sure. The seller is a dealer with their own mechanics, and i've no reason not to trust them, but my plan is to PX these outboards for a new 225 Optimax once I get the boat, so I need to be sure they're PX-able.
 
I've never owned a twin o/b boat but have been in plenty, and that does sound weird, especially if as you say it got worse. I don't know what it is.

500hrs in a 2010 outboard boat is quite good going
 
jfm said:
500hrs in a 2010 outboard boat is quite good going
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Yep, though having seen the fabulous cruising right on their doorstep in Athens, and experienced a winters day equivalent to a summers day here, it doesn't surprise me at all.

Dealer has now hinted at maybe selling the boat without engines, which would be perfect for me, as it removes any risk on the PX. I think i'll pursue that option on Monday.
 
That does sound a bit out-of-balance.
12s is about the point where the throttles are increased a bit.
A compression check on each engine would be a quick and cheap health check if you weren't sure.
 
Received a response from the dealer, who thinks it's just that they were out of sync:

The “steam train” noise is clearly the result of the two propellers coordinated revolving.
If you had asked about that yesterday I would have tried the boat for you with only one engine running (either one) and you wouldn’t hear that noise!

The engines on this boat are set up with a 17 mm convergence, as we have found that steering is optimal this way and no unnecessary stress is put on the silent blocks of the engines.
This may produce the “steam train” noise in greater effect than if the engines were parallel.

Also, in low revs, even a small difference between the two engines’ RPMs affects the overall audible sound.
 
Nick_H said:
Yep, though having seen the fabulous cruising right on their doorstep in Athens, and experienced a winters day equivalent to a summers day here, it doesn't surprise me at all.

Dealer has now hinted at maybe selling the boat without engines, which would be perfect for me, as it removes any risk on the PX. I think i'll pursue that option on Monday.
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Nick,
you were slightly lucky, up here it was almost 20C yesterday and Athens is usually much milder.
I'm impressed with the 500h though, that much have been tons of petrol at 1.5+euro/lt when many ppl couldn't afford to use their craft this year...
Area is perfect during the winter and pants during the summer with zillions of ppl in the beaches, 35+C, traffic, et al :p

cheers

V.

PS. there's also decent food available JTB
 
vas said:
Nick,
you were slightly lucky, up here it was almost 20C yesterday and Athens is usually much milder.
I'm impressed with the 500h though, that much have been tons of petrol at 1.5+euro/lt when many ppl couldn't afford to use their craft this year...
Area is perfect during the winter and pants during the summer with zillions of ppl in the beaches, 35+C, traffic, et al :p

cheers

V.

PS. there's also decent food available JTB
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The owner has a holiday home on one of the islands, and spends much of the summer there with the boat, so avoids the crowds and traffic.

I wasn't joking about the decent food, we had some delicious kebabs, then ended up in a great bar in the shadow of the Acropolis with a band playing traditional Greek music.
 
Nick_H said:
Is this just down to the engines being out of sync? It seems a lot of noise just to be caused by that, but i've never had a twin outboard boat so I dont know for sure. The seller is a dealer with their own mechanics, and i've no reason not to trust them, but my plan is to PX these outboards for a new 225 Optimax once I get the boat, so I need to be sure they're PX-able.
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Nick the Vid is too short to suss out if anything is really wrong
I will add this, that when you have twin outboards or even two engines of similar type operating closely
You will experience/hear the 'Doppler effect' (google it mate), I first experienced this without knowing in the 60's whilst following my mate on my two stroke trials motorcycle down a narrow lane.
It was weird, at one time our exhaust 'notes' where in sync then sometimes they were not.
This experience led me to 'listen' to engines of proximity in later years
I have used twin outboards on a few occasions Commercially(trip boats etc) and quite often they seem out of sync because of the phenomenon described earlier.
Check if they both tickover at the same revs
Check if they both accelerate similarly individually
oh yes they are PX-able 140 outboards and similar size are very desirable on the used market
 
Hi Nick, I have twin 250 Yamaha's on my boat which are V6's and as a result are very smooth. The video on first listening does set any alarm bells ringing and is still a lot quieter than running a pair of Mercury Optimax 150's for example. The Suzuki 140's which are a 4 cylinder I think are a popular engine, and a chosen power unit amongst the Rib community. If you don't get any luck on this forum www.rib.net/forum may be able to help out?
 
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I think what some are trying to describe is heterodyne, when 2 dissimilar frequencies overlap, and you get a droning effect. I used to get this on my Sunline if I hadn't set the throttles correctly, and you end up with an annoying effect. Simplest way to check is to change the throttle setting on one of the engines.
 
btw, the video clip sounds exactly as the sound I get from my BMW X3 sunroof windprotector thingy that starts flapping ever so slightly at a certain speed (which I don't even remember any more as the car's sat in the garage with a suspected cracked block and massive appetite for coolant for 8 months now...)

cheers

V.
 
I've just agreed to purchase the boat without the engines, which is ideal as it removes any risk on the PX.

I'll post details of the boat on the original thread.
 
vas said:
btw, the video clip sounds exactly as the sound I get from my BMW X3 sunroof windprotector thingy that starts flapping ever so slightly at a certain speed (which I don't even remember any more as the car's sat in the garage with a suspected cracked block and massive appetite for coolant for 8 months now...)

cheers

V.
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Heterodyne Vas. Well known on cars when you crack a window open, coincident frequencies set off some unpleasant noises.
 
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