thrust and bhp

[Charles uk]

I've only see 2 of these & only 1 in operation, & that was fixed in a fnr type transom bracket & that gave a reading like you'd expect.

[Adrian Dale]

The weather being perfect for a test run yesterday I headed out on the water to do some trials

Calculated boat speed of my Dingy 4.04 Knots

The "course" I chose was north through the D'Entrecasteux Channel to a friends jetty in Great Daniels bay a distance of 8.12 Kn miles one way.

The Engine originally selected was the LS 18407. Unfortunately despite running soundly in a test tank It was less than happy on the back of the boat. The original 'U' fuel supply pipe failed at the nipple due to metal fatigue. An unfortunate fact with a 60 year old engine. So a brisk row back to the jetty was involved and a change of engine. This was rather a disappointment because I had particularly wanted to get some performance figures for the LS.

Not wanting to wast the day I used my 76 FP.
Time one way 1hour 55 minutes with one fuel stop 2 minutes Average speed for the run 4.25 Kn miles/hr. Fuel used 2.9 litres.
Gear box oil check: box full of what appeared to be a good emulsion. Box not drained or topped up but more on this on the return leg.
Sea conditions flat calm with light zephyr of breeze

Time on the return leg ( After one hour stop.) 2 hours exactly with one fuel stop of 2 minutes. Average speed for run 4.04 Kn miles/hr Fuel used 3 litres
Sea conditions small wavelets with wind up to 10 Knots (The first 1/2 hour of the return leg the wind and waves were on the stbd beam thereafter on the stern.

The engine preformed perfectly both ways.

Only Problem the gearbox oil. On draining the oil off to inspect the condition after what amounted to a 4 hour not stop run it was found to be the consistency of soft grease, although still just fluid. As it drained it was observed that no emulsion had occurred and the sea water trickled out clean and uncontaminated. This is not what is wanted and I suspect that with any longer run time the gearbox would have suffered damage.
The Oil used was Penrite Gear Oil 140 EP.

In the excellent Post of the Murray River transit last year, it was stated by the participants that this gear oil was not suitable for long trips and that is again confirmed here. The oil is specifically designed not to emulsify, great for modern sealed machinery, not good for unsealed gearboxes. I see in back posts that there are many suggestions but I have yet to locate a satisfactory oil here in Australia, although I am sure one is available. Penrite is readily available in most chandlers so easy to obtain.

AJ

[Collector Inspector]

Interesting Adrian

What colour was the emulsion?

B

[Adrian Dale]

It didn't emulsify and remained light blue all be it with a higher viscosity..

AJ

[Collector Inspector]

Blue is correct...............well looks like speerment milk........ not coffee with none aye.

I have used the 90 weight version of limslip with no problems for ages so maybe the viscosity may well be a factor with water not mixing at the "End"?

This is a pic of one of the earlier containers saying 140. As above I used the max 90 version of back then.

Limslip_2011.jpg (27.04 KiB) Viewed 3259 times

Maybe they have changed the mix as "Limslip" does not seem to be available "The Same" now.

Maybe revise oil replenishment for the future who knows?

Cheers

B[/color]

[Adrian Dale]

Correct the limslip has been discontinued. basically the replacement is a better oil if you don't want an emulsion. Replacing the oil is no problem if its a short run but I am planning a run around Bruny Island a distance of 75 Kn miles non stop so cant change the oil..

AJ

[Charles uk]

Talk to the oil suppliers that supply the mining & old saw mill industry I was given 4 pints of SAE 460 last year, & try to stick with the SAE types, they don't seem to have the additives that prevent it forming an emulsion.

[Adrian Dale]

Yes but that is very heavy did you cut it?

AJ

[Charles uk]

No, it was the oil nipple gear boxes, it wasn't as gooey as you'd expect.

[1charan]

The weather being perfect for a test run yesterday I headed out on the water to do some trials

AJ

Yo Adrian,

Why are you hijacking my topic???

[Adrian Dale]

No not really, I was interested in your comments re the two engines and their power when tested against boat speed and therefore a good long test run was needed to confirm the connection re calculated speed and actual speed. What I can't calculate from that is the power it requires to reach boat speed, however with a known engine with a correctly rated power output a close approximation could be achieved by direct ratio.

The gearbox oil was a side issue but If you are going to run for long periods a more compatible oil is required.

AJ

[Rob Ripley]

Just a question ...

Does the thrust change (at WOT) from when the boat is tied to a bollard to when the boat is moving a maximum hull speed ?

[Charles uk]

Yes it does!

If you tie your boat to the jetty & put it in gear you will find your maximum revs at WOT are (at a guess 3200) depending on gear ratio & prop.
Now untie your boat WOT & it's reaching ( guesstimate 3840).

So an extra 640 power strokes of the piston each minute, which would imply it's putting 20% more power into the water & that might be getting on for 20% more thrust.

Ignore the hull speed as just about all Seagulls can exceed displacement hull speed on dinghy hulls, & then turn into semi displacement hulls.

[1charan]

Yes it does!

If you tie your boat to the jetty & put it in gear you will find your maximum revs at WOT are (at a guess 3200) depending on gear ratio & prop.

What I like about this Static Bollard Pull is that you take the boat out of the equation. As long as the propeller is below the bottom of the boat, the numbers are comparable with anybody else's numbers. I agree with Charles that it is not a real world test because the water flow is different. But at least it is something.

[Charles uk]

What I like about this Static Bollard Pull is that you take the boat out of the equation. As long as the propeller is below the bottom of the boat, the numbers are comparable with anybody else's numbers. I agree with Charles that it is not a real world test because the water flow is different. But at least it is something.

Providing your using the same gearbox & prop.