Overheating

SteveGorst

SteveGorst

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I have read several posts on the forum about overheating. One good tip I came across was to check the diameter of the water intake. After blockages have been discounted. However nobody seemed to mention prop pitch. My beta engine should rev up to 3600 revs. However it only revs up to 2300. The boat does go just over 6 knots at those revs, Moody 33, but if I hold it at those revs for any length of time it overheats. Backing off to 2000 revs and 5.6 knots cures it, and I can live with it, but its not right. The boat is new to me and I haven't had it out of the water to check the prop size yet but would the forum agree that taking an inch off the pitch, whatever it is, would be a good idea?
 
You are seriously overpropped and will wreck the engine if you continue running like that. The Moody 33 is a difficult boat to re-engine as it originally had a direct drive (1:1) because there is only clearance to run a very small diameter steep pitch prop.

Suggest you ask Beta for a recommendation for size as i am sure they will have records of what works. You should be able to achieve at least 3400 and get close to 7 knots, cruise at around 2400 and 5.5 knots.
 
SteveGorst said:
I have read several posts on the forum about overheating. One good tip I came across was to check the diameter of the water intake. After blockages have been discounted. However nobody seemed to mention prop pitch. My beta engine should rev up to 3600 revs. However it only revs up to 2300. The boat does go just over 6 knots at those revs, Moody 33, but if I hold it at those revs for any length of time it overheats. Backing off to 2000 revs and 5.6 knots cures it, and I can live with it, but its not right. The boat is new to me and I haven't had it out of the water to check the prop size yet but would the forum agree that taking an inch off the pitch, whatever it is, would be a good idea?
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Reducing pitch to ensure the engine reaches max designed revs at max speed is a good idea but only if you have a perfectly clean bottom and prop at the time of the test. However, i dont think this will cure your everheating problem. Even if you are not getting full revs i would still expect the cooling system to maintain the correct temperature. If i were you i would eliminate all other reasons for overheating first before changing the prop. Did it ever work correctly in the past with that prop?

Www.solocoastalsailing.co.uk
 
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I also have a Moody33 which I re-engined with a Beta 25hp. The prop is 13x10, and I only rev up to 3300 when first launched. I keep saying to myself that I should get the prop re-pitched to to 9½ but I have not got round to it yet. It was a bit of a guesstimate when I fitted the engine as I also had to have a new prop as the Beta need the opposite rotation. I could not have a larger prop as 13" was the largest prop that could be fitted without cutting a groove in the hull! (or completely re-aligning the prop shaft and engine)
I think you should check the prop - can you dry out against posts or harbour wall to avoid a lift out? Check what pitch it is and get a prop manufacturer to check what size prop you should have. If the prop is clean it sounds as if the prop is completely wrong.
Another point - on my previous boat, on a trial sail, the owner said he never revved about 2500rpm. After I bought the boat I discovered it would NOT rev above 2500rpm! On inspection there was a tiny in-line filter in the fuel line which was completely blocked with gunge and when removed the engine went to 3600rpm! If you need more info just pm me.
 
Leaping to the conclusion of wrong prop size seems a bit of a forum habit?
How does the engine behave at full throttle? Smoke?

I would suggest checking the flow rate of the seawater side. Perhaps run the motor with it pumping from a bucket.
Or collecting it from the exhaust with a bucket. If you do this, let the revs settle for a few minutes, to stabilise the amount of water in the exhaust, and/or average a few readings. There should be a figure for the proper flow rate at some rpm or other?
You could have a partial blockage in e.g. heat exchanger or mixing elbow.
The impeller pump could be worn.
The water intake side is also worth looking at, it could be fouled. Is there a big plastic strainer? sometimes those let air into the system .

Also, one could ask Beta, they might know who they sold the engine to, and that might tell you about the prop etc?

The engine should not overheat, even with the wrong prop. It's a lot easier to sort that in the water while you can test it properly.
The performance may be a separate issue, it could simply be fouling?
 
6 knots ? 5.6 knots ? what does it matter. You have a sailing boat not a mobo.
Sounds like a fuss about nothing.
 
Sandyman said:
6 knots ? 5.6 knots ? what does it matter. You have a sailing boat not a mobo.
Sounds like a fuss about nothing.
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And in flat water and calm conditions, you're probably correct. But if the OP is, one day, caught out in storm conditions with a disabled sail and really needs that engine he will probably regret having a seriously oversized prop, if that's what he has. :ambivalence:

Richard
 
Thanks for the replies

The engine doesn't actually smoke at full throttle but it does overheat. My theory is if the engine is more free revving more water is pumped through to keep it cool. When it has to work hard at low revs it is generating a lot of heat but its not getting the cooling water it needs. The impeller has been changed and the waterways cleared of debris the engine is 7 years old 400 hours. I don't actually have to buy a new propeller as I have a Propeller specialist nearby that can re pitch it by up to 2" so I don't expect that to be a major expense. At the moment there is no visual check on water flow either. The exit is below the hull. I will fix a vetus strainer so I can check the water is flowing freely. On previous boats I have had over propping has caused overheating so as well as checking everything else I think I will re pitch to cover that.

The 5.6 vs 6 knots is something I can live with as I stated but the revs and the overheating are the concern. Sometimes by pushing through a tidal gate like the calf sound in the Isle of Man one can save hours of waiting and achieve passages that would otherwise not be possible and there are occasions when one needs everything if only for a few minutes without worries of overheating.

As stated the hull may be dirty as well but she does sail well, we were beating upwind into 20 knot apparent at 6.5 knots the other day.

I will post updates as I work on it...
 
The engine should be able to give all the power it can at any rpm without overheating.
So I suspect you have a bit of a cooling system issue.
If you re-prop, your may never see the cooling system issue until something makes you need max power for a while, like as you say motoring into weather to make a tidal gate.

A lot of people seem to like their boats tending towards 'over propped', nice and quiet motoring at lower rpm when there's no wind.
You'd have to overdo that quite badly to get the numbers you're giving.
What size is the engine?
Is there any other reason to suspect it might be 'unwell'? does it start well etc?
Losing power for any reason get the 'won't rev' problem.
Losing power and overheating,,.. I can't think of too many things that would cause both.
Injector timing and exhaust back pressure perhaps?

I think knowing what prop you have, doing the maths and seeing if it explains where you are is a good start.
 
One other check for you may be to see if a strainer grid is fitted below the water intake .At this time of the year the mussels seem to deposit their offspring both inside and outside of these, reducing the intake to the impellor.
I also check my raw water intake to the loo which has one of these, and in spite of anti-fouling it manages to cut down the intake of water when flushing. Whilst Blue Duck works here, it isn't an option for the engine.

ianat182
 
lw395 said:
The engine should be able to give all the power it can at any rpm without overheating.
So I suspect you have a bit of a cooling system issue.
If you re-prop, your may never see the cooling system issue until something makes you need max power for a while, like as you say motoring into weather to make a tidal gate.

A lot of people seem to like their boats tending towards 'over propped', nice and quiet motoring at lower rpm when there's no wind. - I agree, a friend of mine is proud of getting 7 knots at more or less tickover, as soon as the weather turns poor he can barely move for cavitation... and he overheats...
You'd have to overdo that quite badly to get the numbers you're giving. - I think it is, I phoned Castle Marine who are the local propeller specialists this morning and he says I am seriously over propped so as you say I think this is a good starting point and needs doing even if it doesn't cure the overheating. I will be surprised if it doesn't though. They are going to reduce the pitch by 2". I'm taking her out of the water next month for a couple of weeks so should know the result after that.
What size is the engine? - its a 35 horse Beta 7 years old 400 hours, barely run in...
Is there any other reason to suspect it might be 'unwell'? does it start well etc? - yes it starts fine, it just switches on like a light on the first turn. New filters fitted.
Losing power for any reason get the 'won't rev' problem. - no loss of power the boat reaches hull speed and loads of wash coming out of the back trying to push it faster.
Losing power and overheating,,.. I can't think of too many things that would cause both.
Injector timing and exhaust back pressure perhaps?

I think knowing what prop you have, doing the maths and seeing if it explains where you are is a good start. - yep I agree I'll let you know how I get on :)
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ianat182 said:
One other check for you may be to see if a strainer grid is fitted below the water intake .At this time of the year the mussels seem to deposit their offspring both inside and outside of these, reducing the intake to the impellor.
I also check my raw water intake to the loo which has one of these, and in spite of anti-fouling it manages to cut down the intake of water when flushing. Whilst Blue Duck works here, it isn't an option for the engine.

ianat182
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Yes this used to be a nightmare on my old saildrive. I could have had a good meal with the crop in it each spring. I will check for this and also check the diameter of the inlet to see if it matches the diameter of the water pipes on the engine.
 
According to the Beta datasheet, peak torque is at 2100rpm and 35hp is at 2800rpm. Or is that a different engine?

I still suspect there is more than a pitch problem here.

I would find out what prop you have
try that with the engine data in the various prop calculators
does it stack with reality?
i.e do the models agree on 5.6kt @2000 rpm and 6 @2300?

You can do this manually, by estimating the drag of the boat based on its lwl etc, and a set of prop graphs from a suitable book.
If you look at the numbers, the prop is only slipping a small amount more at the higher rpm. This may not be consistent with too much pitch?
Is there a lot of blade area? Is it a 3 blade?

It would be galling to cut metal and not cure the problem, so doing the maths first would be my approach.
I object when people leap to the conclusion of wrong prop with spares information, as you may have guessed.
(I also believe all sailing boats should have folding or feathering props of course.)
 
yes it is a three bladed propeller. I dont think it is slipping as such just working too hard at low revs. It looks like it is reaching its peak torque but not managing to get past that. I thought I had read somewhere that it was supposed to reach 3600rpm as my old beta but it appears the 38 is 3600 and the 35 is 2800 so it may not be as bad as I first thought prop wise.

I definitely will check all the water supply possibilities. I have cleaned debris from the heat exchanger inlet but not actually taken the heat exchanger out to check the tubes. I'll put that on the list for this weekend. Also the propeller may be covered in Barnacles so I may dry her out against the wall and see.
 
Clearly the fresh water circuit is over heating, but is the sea water part also overheating, if it is then the sea water may not be carrying away the heat probably through poor flow or crud in the heat exchanger. If the sea water part is OK then the problem lies in the fresh water part, possibly problems with the water pump or poor circulation in the block which can probably be cured with radflush
 
SteveGorst said:
yes it is a three bladed propeller. I dont think it is slipping as such just working too hard at low revs. It looks like it is reaching its peak torque but not managing to get past that. I thought I had read somewhere that it was supposed to reach 3600rpm as my old beta but it appears the 38 is 3600 and the 35 is 2800 so it may not be as bad as I first thought prop wise.

I definitely will check all the water supply possibilities. I have cleaned debris from the heat exchanger inlet but not actually taken the heat exchanger out to check the tubes. I'll put that on the list for this weekend. Also the propeller may be covered in Barnacles so I may dry her out against the wall and see.
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The 35 is governed to the lower revs - that is cannot be fuelled to exceed those revs. so if your engine is governed to 3600 and you can only achieve 2500 it is being overfuelled and will have a tendency to overheat. By all means check the water inlet - it should be 3/4" from memory, but if the intake hose is the same all the way through with no step down it will be the right size.

It is a condition of most engine warranties that the engine does meet the minimum, which i guess for a 3600 engine will be either 3300 or 3400, precisely because overpropping can lead to damage and a rejected warranty claim. On my new Volvo D1 the minimum is 3000 out of 3200. On trials with the Volvo commissioner we paid particular attention to this because I had fitted a non standard prop. Fortunately got the sums right and achieved 3100 and speed of 7.5 knots.

As I suggested earlier you should aim for at least 3300 and over 7 knots. You may just be able to achieve that with 2" less pitch.
 
I have checked my paperwork and the version of the 35 that I have should indeed rev up to 3600 as I first thought.so I will repitch. Perhaps the previous owner got confused and pitched it for 2800 revs.
 
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