Overheating Engine

[Adams10]

We have recently replaced our 20 year old Drofin diesel auxiliary on our Adams 10 yacht with a Beta Marine 20hp Kubota. We have also fitted a new geared two blade folding propellor. The Adams 10 is a cruising version of a 33ft "in shore" racing yacht which has a relatively light displacement, narrow beam and fin keel.
The engine is rated at 20hp at 3600 rpm and has a 2 to 1 gear ratio.
We have found that we can only get 2700 rpm out of the motor under load in flat water. The motor will run indefinitely at 2200rpm but when we push it at the maximum speed of 2700 rpm for 20 minutes the temperature warning light and buzzer come on. We have a 3/4" water inlet and have removed the strainer but the problem persists. Is it likely the overheating is due to propellor mismatch.

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[alan]

What are the maximum revs you can obtain with the engine being run in neutral? I would guess that you should be able achieve around 3100/3200 max for an engine rated at 3600. (My VP2020 has a similar rating and achieves this.)

My boat is fitted with an Autoprop and when the prop is clean and shiny, I can achieve around 3100/3200 revs maximum "in gear". When the prop is fouled I can only achieve around 2700revs maximum "in gear".

Perhaps your prop is not correctly pitched; either not adjusted correctly or just plain fouled (growth e.t.c.) which is preventing it achieving the correct pitch??

No doubt you will get more informative replies, but my guess would be the prop pitch.

Good luck.
Alan.
Nettuno, Italy.

<hr width=100% size=1>Alan Cloke

 

[Adams10]

Thanks for your prompt reply. We can get run in excess of 3600 rpm in neutral. The engine is new, as is the propellor and the boat and prop were antifouled before putting the boat in the water.

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[alan]

If you can achieve the 'correct' revs in neutral then it must be something to do with gearbox/shaft/prop. As engine/gearbox is new then my guess is the prop pitch or even size.

Are you sure the prop is correct for your combination of engine/boat. Perhaps a call to another prop manufacturer (not the one who supplied your present prop) would be a useful check. They can usually advise you of size/pitch e.tc. immediately from their database.

Could it be that there is antifoul on the prop gears preventing it opening fully??

I'm afraid I don't know enough about it to advise further but I'm sure someone will be able to advise on 'correct' size and pitch for this combination of engine/boat.

Alan.

<hr width=100% size=1>Alan Cloke

 

[dickh]

Certainly sounds as though you are overpropped. I have a 18HP perkins - same as the VP 2020 and when I got it(secondhand) it would not rev above 2800 when under load and just launched. The prop was 2 bladed 15x9, with a 2:1 reduction g/box. I had the prop repitched to 15x8 and it now achieves 3250 under load just launched. The max revs are 3600 when not in gear. I'm happy with this although I suspect if I went to 15x7½, Iwould achieve a max speed of 3500.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[brianhumber]

Assuming new installation is correct, sounds like a re-prop job is needed to match torque and speed available from new engine to what the prop fitted demands.


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[snowleopard]

i've just run your data through the prop tables and, assuming you would be making 8 knots flat out in smooth water with the data you have given, the ideal prop size would be 13-14" dia by 9" pitch. how does that compare to what you've got? it certainly sounds as though you are way over-propped.

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[roger]

Its also worth checking that the exhaust is of the rquired size. I think its 51 mm ID

<hr width=100% size=1>Roger

 

[gtmoore]

Not sure if this is any help but my 2p worth is that our 29ft (25ft LWL) boat has a Beta 722 20hp (2:1 box) and when we bought her she was fitted with a 15x13 2 blader which only allowed us approx 2500rpm. It shifted us along at close to 6 knots however and even after some extensive use of the engine last year we didn't suffer any overheating problems. I always felt we were over propped especially as the boat supplied with the original Buhk 20hp was fitted with a 13x13 2 blade.

I've since changed the prop (for other reasons) to a 13x9 3 blade which allows the revs to go close to 3500 and from early indications we are doing around 7 knots at about 3000rpm. There also feels much less turbulence under the hull which used to be quite apparent through the tiller with our transom hung rudder


<hr width=100% size=1>Gavin

 

[sailorman]

if u visit the Nanni site they have a "prop size" chart its not exact but a reasonable guide

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[Heckler]

bottom line is that no matter what revs the engine is doing and whether overpropped or not (if you are getting 2700 revs its not that far out) it shouldnt over heat. the problem lies in your cooling set up, sort that first then sort the prop size.
stu


<hr width=100% size=1><A target="_blank" HREF=http://www.beneteau-owners-association.org.uk>http://www.beneteau-owners-association.org.uk</A>

 

[oldharry]

Firstly over propping will definitely not cause the engine to overheat. So there is a problem elesewhere. The engine manufacturer will specify the minimum size for water supply pipes to the engine, so this is the first thing to check. An undersize exhaust pipe can reduce the power output, but again would not cause the overheating problem.

Assuming there is sufficient cooling water supply, and overheating is still occuring, then there is a fault with the engine - most likely either the pump timing or the camshaft/valve timing is incorrectly set up. Setting the injection timing requires the use of accurate measuring tools, and needs to be checked by a trained mechanic - unless you know how to do it yourself and have the tools. Checking the camshaft timing is usually simple enough if you know where the timing marks on the cam and crankshafts are (see the workshop manual).

You need to ensure all is well with the engine before changing propellors etc. The low revs on power, coupled with overheating does suggest they could be something else wrong. Full revs off load means simply that the injector pump governor is Ok, and that there is no major mechanical fault!

Check also for tightness in the gearbox, and or sterngear which could be absorbing the power, if none of the above shows anything up.



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[Adams10]

I have checked our records and the propeller fitted to our Adams 10 is a 14" x 10" geared folding two blade propeller.

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[Adams10]

I have checked my records and the new prop fitted to our Adams 10 is a 14"x10" geared folding propeller.

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[cliff]

I had a similiar problem with the BETA 20 overheating on my previous boat (Jaguar 27) when the throttle was opened full. I would recommend you check the level of coolant in the fresh water side and top it up with 50/50 glycol/water mix as per the instruction that came with the engine. The over heating problem only happened to me when the coolant level was low. Dont ask me where the coolant went but I had to top up (about a cupfull or two) every 2 to 3 months - never could find any leak. After topping up I could run the engine hard and no problem. I achieved hull speed at around 2200rpm so running the engine harder gave little increase in speed also never managed to get engine above 2900~3000 (engine was over propped).

Might pay to check the water intake filter, seem to remember once getting some gunge into it also check the exhaust discharge. Broken impellor maybe? Enough oil in the sump?. many things can lead to overheating worth checking them out before looking at the compatibility of the propellor. I always found the 20hp Beta to be very reliable and responsive.

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[roger]

In the Beta manual they give instructions - I think - about measuring water flow by collecting same in a bucket hung below the exhaust. Compare the amount with the recomended value or ask Beta. They do warn you to be careful in case you poison yourself with the fumes.

<hr width=100% size=1>Roger