Lack of torque?

[amf]

Am I being paranoid? Sorry for lengthy history but here goes:

Bought boat (S23) September last year from new. Has a single KAD32. Beginning of this year had a problem with the engine not wanting to go above about 2000 revs. Problem was fixed under warranty (compressor relay broke).

Had similar problem about 2 months later. Again was fixed under warranty and explanation was that they had found an air leak? Went on test run with engineer and engine picked up quickly all the way to 3800 revs (WOT) with 3 adults on board.

Had similar problem again in beginning of July just as we were about to embark on a West Country cruise. This time problem was barnacles on prop and drive (after 3 weeks of non-use). Had the boat lifted and blasted. This time I had to pay (fair enough).

After the last episode max revs seems to be around 3600 - difficult to explain but engine seems to lack torque - especially if boat is fully loaded (water, fuel, adults etc).

Was out at weekend with 4 adults in boat. Revs went up to just below 3000 and stayed there - boat struggled to get on the plane. Used a bit of trim tab and boat got on plane and revs then increased above 3000. I didn't go WOT as it was first time out for our guests.

Is this expected behaviour? I always imagined that a heavily loaded boat, unlike a car, would not effect revs - just the amount of slip the propeller produces.

So, question is (phew!) - I have 1 month of warranty still to run on the KAD32. Do I get the dealer to check engine again and probably incur further costs or do I wait until next season once the hull/drive/props have been cleaned and polished?

Best scenario is that it is just down to props/drive not being totally clean - worse scenario is that its an engine fault that's been there since new that will no doubt cause major problems a few days after the warranty runs out!

- Andrew

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[markc]

Loading and hull fouling certainly affect my RPM....all clean & light will spin upto 2600, a few weeks ago only 2100 (before Dave the Diver sorted out the crap under water!)

Mark

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[[2068]]

Part of it is that the duoprop doesn't slip much, which is fantastic when you are overpowered and want max acceleration. In the case of a KAD32 driving a 2.5tonne boat plus 4 adults, fuel and water, a bit of slip would probably help.

As comparison, on the S24 with the same engine, with full fuel&water plus 4 adults, it normally needs some trim tab to get planing, which then get eased off as the speed increases. WOT is 3750rpms at the start of the season, which then drops slightly as the hull goes slimy, props get a few dings & barnacles, etc. etc.


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[burgundyben]

I think fouling has been a particular issue in port solent this year, go for a run somewhere shallow and sandy like over near ryde, drop the hook in a 4 or so feet and jump in an clean the bottom, or use boat scrubber or have her lifted and cleaned, reckon that will tell you if there is another fault.

weekly this time of year there is posts like this, drop off in performance etc, generally its due to dirty bottoms.

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[adarcy]

Agree with Mark.

If you're dirty the prop cannot thrust the water back fast enough to reach peak revs (and therefore area of peak power). Think of it like increased hull etc drag prvents the prop screwing through the water fast enough.

Ours can drop from max 2700-2800 down to 2400 max by the end of the season.

BTW it may be that your power is a bit marginal to expect it to hop up on the plane when well loaded and dirty without trim tab help. Of course others have to do it all the time see another thread

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[amf]

Thanks. Always good to have comparison with same (similar) boat. Didn't realise the duoprops were that efficient!

Cheers

Andrew

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[ArthurWood]

If revs have dropped, always check condition of props first, then hull.

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[mjf]

I reckon the bottom contributes relatively little to the problem - The issue is the props.

I therefore agree that an hour in shallow water with a scraper and wire wool will do the trick - if you have the energy thereafter do the hull.....

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[Aardee]

If you're in Port Solent then you'll definitely need a scrub. Fouling has been a real issue this year!!

Graham.

<hr width=100% size=1>"I am a bear of very little brain and long words bother me" - A A Milne.

 

[amf]

Yeah, had a scrub at beg of July - Props look OK when I raise the outdrive but difficult to see back edge of blades. Still some muck on the outdrive and trim tabs though. I am hoping this is what is causing loss of revs.

- Andrew

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[longjohnsilver]

Make sure you wear gloves when cleaning props, it's very easy to cut yourself and not realise it.

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[mjf]

Excellent point - also if you do damage your hand the thing takes forever to heal - something in the make up of coral / barnies etc

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