Prop shaft seal running hot?

[Tranona]

So I replaced with a new transparent hose and ran it above the water line. Before I fixed it I let a few litres of water out making sure there is no air left.
After one hour of motoring the edge was again ~70-75 degrees C, the body about 40. So there is no change.
The temperature did not continue to climb past that mark. Next I will try to run forced cooling either from the cooling water from the engine, or just a small 12v pump with a fresh, cold sea water and see how it changes things..

What size is your prop shaft? The seals are made in both metric and imperial sizes and they are not interchangeable. For example if you have a 1 1/4" shaft the metric "equivalent" is 30mm which may just slide on but will be too tight. Does the shaft turn freely when not in gear? Also although you have checked there is no air in the system when static, have you checked that water can flow out of the aft end of the stern tube?

 

[Pye_End]

Also although you have checked there is no air in the system when static, ?

Would you expect the outer seal to be wet when the inner seal keeps the sea out?

 

[VandKoala]

What size is your prop shaft? The seals are made in both metric and imperial sizes and they are not interchangeable. For example if you have a 1 1/4" shaft the metric "equivalent" is 30mm which may just slide on but will be too tight. Does the shaft turn freely when not in gear? Also although you have checked there is no air in the system when static, have you checked that water can flow out of the aft end of the stern tube?

I have measured the shaft before ordering the seal. If I remember correctly it was 35mm.
How can I test if the water can flow out of the stern tube? I tried blowing into the tube when motoring and I can blow most of the water out, it returns when I stop blowing in it. The water level in the tube decreases if I motor at 3000rpm VS my tipical 1700-1800.
Next to my stern tube there are tiny water intake bronze pipes, I guess for scooping the water when on the move. I dove down today to try and take a picture, but it is blurry

 

[VandKoala]

Whilst not wishing to negate the answers of others, I would say this. It would not be first time that I have fitted devices to shafts, bearings, seals etc. and found that they ran hot, sometimes very hot, for a period of time after fitting, maybe as long as a couple of hours. The temperature would then drop like a stone and all was well.
Whilst that may not be the case in your instance, if you are sure that everything else, Alignment, cooling and fitting etc. are all correct, then why not just run under load for a while and see if it corrects.

Interesting observation!
Yeah I am not pulling the boat put any time soon again. So I guess I will keep watching while keeping my emergency kit close by (bike inner tube cut open + zip ties)

 

[Dockhead]

You are right - a poor choice of engine. Your boat only needs 60hp (which is what it would have had originally) to achieve hull speed so you will only ever use 50% of the power available. Running at low rpm on such a low load is not good for the life of the engine.

Thread drift, but this is an interesting subject.

I agree that that's too much engine for that boat, but how you figure exactly what is more complicated than this.

First of all, just enough power to drive the boat at hull speed in calm weather and flat sea is not enough power. You need enough power to claw off a lee shore against a strong wind and steep head sea, which is probably twice that much power. 5hp per tonne is not too much; 6 or 7 could be better. Also what kind of prop you can swing makes a lot of difference -- so even here, not all things are equal.

Second, some percentage of power available is not the way to determine a minimum healthy load for a diesel. It's very different depending on displacement of the engine, and what RPM you're talking about. The goal is to have enough load to keep the cylinders warm, and for that the only thing that matters is how much fuel is being injected into a given quantity of air. The 125hp 4JH3-DTE is a 2000cc engine which needs exactly the same load, at the same RPM, as the 56hp 4JH3E, which is also 2000cc, to have warm cylinders. That is, until turbo boost comes on in the DTE, which changes the amount of air passed relative to displacement and RPM, but by that time you're well into the healthy range anyway, so you can ignore that.

The 4JH3 engines are only 2000cc, so it doesn't take that much load to keep them healthy. Maximum power of the 4JH3E at 1900 RPM is only about 33hp. Probably 10hp is enough load at that speed, to keep 2000cc of cylinders warm. The only way to know for sure is with an exhaust gas temperature gauge. You want to keep the EGT above 200C. And the Yanmar manual wants you to run the engine up to the redline in gear every 8-10 hours of operation.

Something like a Perkins Sabre M92 is a whole different ball game. 4400cc and 83hp. No turbo. You need a much larger percentage of max power at any given RPM, to keep that beast from wet stacking.

A big advantage of turbodiesels is they have a much wider range of power outputs which are in the healthy range. It's not hard to keep a 2000cc engine warm inside, then dial up the boost on the odd occasion when you need 100+ hp.

 

[Tranona]

Thread drift, but this is an interesting subject.

I agree that that's too much engine for that boat, but how you figure exactly what is more complicated than this.

First of all, just enough power to drive the boat at hull speed in calm weather and flat sea is not enough power. You need enough power to claw off a lee shore against a strong wind and steep head sea, which is probably twice that much power. 5hp per tonne is not too much; 6 or 7 could be better. Also what kind of prop you can swing makes a lot of difference -- so even here, not all things are equal.

Second, some percentage of power available is not the way to determine a minimum healthy load for a diesel. It's very different depending on displacement of the engine, and what RPM you're talking about. The goal is to have enough load to keep the cylinders warm, and for that the only thing that matters is how much fuel is being injected into a given quantity of air. The 125hp 4JH3-DTE is a 2000cc engine which needs exactly the same load, at the same RPM, as the 56hp 4JH3E, which is also 2000cc, to have warm cylinders. That is, until turbo boost comes on in the DTE, which changes the amount of air passed relative to displacement and RPM, but by that time you're well into the healthy range anyway, so you can ignore that.

The 4JH3 engines are only 2000cc, so it doesn't take that much load to keep them healthy. Maximum power of the 4JH3E at 1900 RPM is only about 33hp. Probably 10hp is enough load at that speed, to keep 2000cc of cylinders warm. The only way to know for sure is with an exhaust gas temperature gauge. You want to keep the EGT above 200C. And the Yanmar manual wants you to run the engine up to the redline in gear every 8-10 hours of operation.

Something like a Perkins Sabre M92 is a whole different ball game. 4400cc and 83hp. No turbo. You need a much larger percentage of max power at any given RPM, to keep that beast from wet stacking.

A big advantage of turbodiesels is they have a much wider range of power outputs which are in the healthy range. It's not hard to keep a 2000cc engine warm inside, then dial up the boost on the odd occasion when you need 100+ hp.

The first part of the question is relatively easy - but it starts at the propeller rather than the engine. You can calculate the propeller size using a formula as in Dave Gerr's book dave gerr propeller handbook pdf although in reality for most "normal" boats prop size calculators such as this vicprop.com/displacement_size_new.php will come up with the optimum size for any given HP RPM and reduction ratio. The aim is to get displacement speed at close to maximum power output which is where the propeller power curve meets the engine power curve. This usually results in a sensible cruising speed at half power/65-70% revs.

The boat in question has a hull speed of 7.7knots and design displacement of just over 10 tonnes. It requires just 48hp to achieve this speed. It was originally fitted with a 60hp Volvo which was more than adequate even when the typical cruising 2 tonnes are added. The propeller would have been probably a 19*11 or 20*10 depending on the reduction ratio chosen. A sensible replacement would be a Beta 60 which would use the same size propeller and give the same performance - top speed of 8.2 knots, so ample reserve. The 125hp Yanmar would in theory achieve a top speed of 10.7 knots!

Modern turbo engines are a waste in this type of heavy displacement boat and grossly overpowering means that the engine will rarely if ever need the turbo.

 

[Tranona]

I have measured the shaft before ordering the seal. If I remember correctly it was 35mm.
How can I test if the water can flow out of the stern tube? I tried blowing into the tube when motoring and I can blow most of the water out, it returns when I stop blowing in it. The water level in the tube decreases if I motor at 3000rpm VS my tipical 1700-1800.
Next to my stern tube there are tiny water intake bronze pipes, I guess for scooping the water when on the move. I dove down today to try and take a picture, but it is blurry

You photo shows maybe 6-8mm gap. At the bottom end of acceptable 15mm is more normal. You might try removing one the anodes to increase the gap.

It seems that there is water in the seal but the flow may not be sufficient and a positive feed from the engine would be a good idea. I don't know whether the temperatures you are seeing are abnormal but the only source of heat is friction from the revolving shaft in the bearing part of the seal. I have experienced this when I fitted a 25mm seal on a 1" shaft, but the shaft was difficult to turn by hand, although the little 10hp Yanmar manged to drive the boat OK. No problem with water flow because the water runs up the flutes. Radice do not seem to make an imperial 1 3/8" which is closest (but a bit smaller) to a 35mm.

 

[snowbird30ds]

I'd tee into the raw water from the engine (after the pump obviously) and feed that to the vent pipe to ensure good flow and burp the seal, to burp just grasp the seal and lift it till water spurts from the top edge, you then also have some water between the lips as well as grease and all air is out, the vent is usually part way along the bearing part so air can still be trapped up by the seal depending on shaft angle.
You can use a drain on the raw water system to take off from.