Possible gearbox trouble - oh woe

[Robert Wilson]

Propcalc give a 12*9 so your 13*8 is about right (1" greater diameter but 1" more diameter is "good")

Your 2 blade is too big diameter as there is not enough clearance as you found. Pitch will not be 2", probably more like 7 or 8.

Your displacement is I think wrong as the figure should be kgs rather than lbs.

The prop size is calculated to achieve close to maximum revs and hull speed at the same time, so you should get around 6 knots at revs above about 3300 (you are a bit short on power for the displacement). This will allow you to cruise at 50% power (or 70% revs - about 2500) at 5 knots.

I couldn't log on to Propcalc, but I did revise my displacement to 7560lbs.
As expected it gives a noticable difference in HP required (17), and prop dimensions (3 blade 11.9" x 6.7" pitch)

I note your comments "a bit short on power for displacement", but I'm comparing "same power train + gearbox" with the new prop.

Very odd, and most disappointing/worrying.
Thanks Tranona

 

[Robert Wilson]

Given the OP reported no black smoke under power, and the prop may not be wildly out, does the fickle finger of suspicion point back towards exhaust blockage (hose collapsed internally?), or fuel starvation (partially blocked filter?)?

As mentioned above, plenty of cooling water from the exhaust, no rise in water temp gauge and new filters (2) installed again, as usual at start of season.

The engine can almost rev its guts out in neutral !!

Thanks once again.

 

[Tranona]

As mentioned above, plenty of cooling water from the exhaust, no rise in water temp gauge and new filters (2) installed again, as usual at start of season.

The engine can almost rev its guts out in neutral !!

Thanks once again.

It will rev to the governor in neutral because it is not under load so producing no power.

A partially blocked exhaust, either the outlet on the engine or the hose is a definite possibility. You will still get normal water flowing and it won't overheat because it is not producing much power. This is a very common problem on small lightly used diesels and well worth investigating.

 

[Robert Wilson]

OK. I'll investigate ASAP.
More crawling around a the engine bay. Rats!!

Thanks

 

[anoccasionalyachtsman]

Whilst you're in there Robert, check that the air intake is clear would you?

 

[Robert Wilson]

Shall do, but I checked it over just before she went in the water.
Thanks.

 

[Pye_End]

FAL give the following data on their invoice:

13" diameter x 9" pitch, 3 bladed, R-H, 0.55 DAR propeller with 1" bore, 2.35" boss, 1/12 taper & 1/4" keyway.

I have a BZ482 with 2:1 and have run it woth a 12 x 9, and a 13 x 8.

The 12 x 9 is better matched, but I wanted a bit more surface area. The 13 x 8 was pretty good, but was a bit over propped for the Beta (max revs I think 3,200 with this). I would suggest on that experience that the 13 x 9 is a significant source of your troubles.

 

[Robert Wilson]

I'm hoping against hope that changing back to the old prop will resolve the issue, but I'm not over-confident.

I should be sailing, not wondering if I have big problems and how to fix them.

Hey ho! - BOATS

 

[John the kiwi]

There is a plate atop the gearbox, but it's been painted over and neglected for a long time.
I'll attack it with suitable tools and solvents, with fingers crossed.

Looks like a long day squirmed into the engine compartment. Oh JOY

Thanks for your advice

I spend too much of my life in industrial plants trying to ascertain what data the obscured nameplates on motors and pumps and gearboxes and other devices once held.
In my view there is a special place in hell for people that paint over these plates! Doubly so if the details have never been recorded anywhere.
Mobile phone cameras have made deciphering these plates a bit easier.
Some plates have the info inked on and its difficult to clean them without removing the data.
Others have the info etched or stamped and its a bit easier.
Start gently with water and detergent only and after cleaning, take photos with illumination (from a torch maybe) from different angles. Then maybe use abrasive scourers but gently and repeat the photography. Try paint strippers but wipe on wipe off quite quickly so if the data you want is inked on it may survive.
Uploading photos to a PC allows you to enlarge and try and interpret.
Good luck.

 

[Robert Wilson]

Thank you for that informative advice I can see a very uncomfortable day ahead

 

[macd]

I'm a bit puzzled, Robert, as to how FAL could even begin to speciy a prop without knowing the reduction ratio. Or did they simply recommend a three-blader equivalent to the old two-blader?

Anyway, good luck with the chore ahead.

 

[Robert Wilson]

To be fair to FAL, 2:1 was the info I gave them having discussed it with the previous owner.
He was a wise man with a lot of experience both with plant and machinery, and sailing. He was a man who knew everything about his boat (now mine) and willingly and patiently helped me enormously with everything to do with Khamsin and sailing around the northwest of Scotland (and the UK).

So, I was happy to pass on 2:1 to FAL

Of course, that's no cast iron guarantee that I was correct

I told FAL about the old prop's closeness to the hull so it was their recommendation for a three bade of the stated dims.

Thanks for your good wishes.

 

[earlybird]

If the gearbox ratio of 2:1 quoted to FAL was wrong then any error would be likely to cause the engine to be under-propped rather than over-propped.
This is based on the assumption that any alternative ratio would be lower, eg 2.5:1, and therefore would not provide an explanation to the OP's puzzle.
I'm not aware of gearbox ratios higher than 2:1 that might be fitted to small engines. Does anyone know differently? I await the OP's findings.

 

[Tranona]

I'm not aware of gearbox ratios higher than 2:1 that might be fitted to small engines. Does anyone know differently? I await the OP's findings.

Yes, all the small engines using the TMC gearbox have the option of 2.65:1 as do Yanmar and Volvo. The Yanmar 1GM also has a 3.1:1 so you can swing a large diameter low pitch prop (just like we did at Seagull). I had that gearbox on the 1GM in my Eventide with a 15" feathering prop with around 6" pitch. The boat now has a Nanni 14 with the same prop and a 2.65:1 reduction.

Not commonly used as most more modern (and lighter) boats of that size using 10-20hp engines are designed to use props in the range of 11-14" and a 2:1 reduction.

 

[Robert Wilson]

Update:-
Yesterday I brought Khamsin alongside to dry-out, removed new three-blade prop and replaced it with the old two-blade.
Refloated, made my way to open water , gave the engine full throttle

No difference.

So, before I start removing gearbox, exhaust hose and anything else I'm going once more to see of there is any malfunction with the Teleflex control and cables.
Clutching at straws, but least of all evils.

I SHOULD BE SAILING, not bu****ing about with propulsion problems.

Grrrrrrrrrrrrrrrrr

 

[peteK]

You will need to check your exhaust elbow for restriction,just because you have plenty of water flow doesnt mean the exhaust gases are not restricted,its a common problem on certain engines and will give the fault you have.
I dont think the gearbox has anything to do with it.

 

[LittleSister]

Others will correct me if I'm wrong (I didn't get to where I am today without being wrong!), but I can't see that the Teleflex controls could be anything to do with it.

If the engine speed control travel was restricted you wouldn't get full revs in neutral, either (it's not a throttle). If the gear control was not fully engaging you'd have different symptoms, was explained by others above in dismissing the clutch slip theory.

I think the forum collective and your prop change has now eliminated clutch slip, gearbox ratio, prop, etc., and you're back to fuel starvation or exhaust blockage as prime suspects.

 

[Robert Wilson]

You will need to check your exhaust elbow for restriction,just because you have plenty of water flow doesnt mean the exhaust gases are not restricted,its a common problem on certain engines and will give the fault you have.
I dont think the gearbox has anything to do with it.

Exhaust elbow on the manifold?

Others will correct me if I'm wrong (I didn't get to where I am today without being wrong!), but I can't see that the Teleflex controls could be anything to do with it.

If the engine speed control travel was restricted you wouldn't get full revs in neutral, either (it's not a throttle). If the gear control was not fully engaging you'd have different symptoms, was explained by others above in dismissing the clutch slip theory.

I think the forum collective and your prop change has now eliminated clutch slip, gearbox ratio, prop, etc., and you're back to fuel starvation or exhaust blockage as prime suspects.

I had come to the same conclusion today; full revs in neutral are available and the control lever on the pump goes up against the stop.
I also can't see a gearbox problem because if it was somehow slipping then the revs would increase at a greater rate than the boat speed.

I am inclined to agree with you both. For process of elimination I'll try the throttle first (hoping against hope, in vain, I fear).

I shall then disconnect the exhaust hose and visually/mechanically inspect.

I calculate replacing the hoses would be a less expensive option than new Teleflex cables etc., although seeing where and how they run from manifold to through hull I think I'm in for a Houdiniesque hour or four!

Thank you both.

 

[Robert Wilson]

Is the potential blockage likely to be nearer the engine end of the exhaust pipes, in or near the waterlock/silencer or towards the through-hull fitting?

And what am I looking for - soot, oily gunge, collapsed rubber piping or a "foreign body" somehow dislodged?
Or all three?

It would help me to know this as I'm totally ignorant of the concept.

TIA

 

[pvb]

Is the potential blockage likely to be nearer the engine end of the exhaust pipes, in or near the waterlock/silencer or towards the through-hull fitting?

And what am I looking for - soot, oily gunge, collapsed rubber piping or a "foreign body" somehow dislodged?
Or all three?

It would help me to know this as I'm totally ignorant of the concept.

TIA

I think people are suggesting that the exhaust elbow (where the exhaust from the engine goes into a rubber pipe) might be partially blocked by deposits. This might be a possibility, but I'm somewhat sceptical as you can achieve full revs in neutral, and that's a similar volume of gas.