Gear ratio

[Dave_Knowles]

How can I tell the gear ratio of a Volvo outdrive?

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[powerskipper]

Ask it

<hr width=100% size=1>Julie ,
IMOSHO of course,/forums/images/icons/smile.gif

 

[tico]

290 o/d..... petrol 2.15:1 diesel 1.65:1 (i think)
Why?

<hr width=100% size=1>Been there, done that, got the oily T shirt<P ID="edit"><FONT SIZE=-1>Edited by tico on 23/01/2004 14:22 (server time).</FONT></P>

 

[Dave_Knowles]

I did silly but all it said was "broom broom". I assume it is Swedish.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[Dave_Knowles]

Tico,

I am trying to work out expected speed from different props and the programme asks for the gear ratio.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[tico]

Dave if its castle marine propcalc, it throws up some strange numbers.

Ring Mike Bellamy at Lancing..... his program is spot on (at least it was in my case)

Whats your setup?

<hr width=100% size=1>Been there, done that, got the oily T shirt

 

[Dave_Knowles]

Here goes:

When I bought the boat it had a 15 x 17 long hub and would not reach max revs.

I fitted a 15 x 15 long hub (as sugested) and it mad little difference.

I have now been told the boat would be better with a 14 x 15. I bought a secondhand one of these but they only come in standard hub high speed (whatever that means).

I want to get some idea as to what extra speed I might get with the 14 inch prop.

Details I was putting in were:

Hull: semi displacement
Water line length 7 m
Weight 4,490kg (boat plus crew and fuel estimated)
BHP 130
Max revs: 5,500


<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[tico]

what revs are you getting?
Whats max revs for the engine? i thort it was 4800-5000 for that engine
wot speed are u getting?

<hr width=100% size=1>Been there, done that, got the oily T shirt

 

[Dave_Knowles]

I am getting just over maybe 4700. The Volvo manual quotes 4,800 to 5,500 full load. Speed max 14kts which is not enough really to get up on the plane.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[tico]

Ok
Petrols generally fitted with standard hub (shorter front to back), coz it allows more slip at start than long hub and hence allows petrols to reach the max power point easier.
Diesels use long hub coz they have more torque and can cope with it.
Sounds like you just need alittle less pitch (say 1") in which case the cheapest option is to ask Steel developments to repitch it £35-50 +P&P
With hull/engine combination i would have reckoned 14kts wd be about right
4.5 tonnes / 130 hp(petrol) doesnt equate to high speed and the most oooomph reqd is for that bit over the
'hump'
Bear in mind that V**vo's claimed 130hp probably is closer to an actual of 115-120hp.

<hr width=100% size=1>Been there, done that, got the oily T shirt

 

[Dave_Knowles]

So you think the 14 x 15 should be worth trying? What does the high speed (Volvo description) mean? What reves do you think I should expect as max?

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[tico]

The 14x15 std hub is worth trying coz youll get a rev increase twofold, 1 coz the smaller diameter will allow greater slip and 2, the shorter hub will do the same because the blade area gripping the water is less. I would expect youll get 5000-5100rpm which will allow the engine to develop a bit more power.
Speed i guess maybe up a couple of kts but its a compromise between developed engine power which is more offset by the greater slip of the prop.
Volvo calling their props 'high speed' just refers to power boat ones rather than displacement/raggie ones.
However, its very important for best effect that the prop is in good shape. 'dings' and chips will dramatically affect performance. If in doubt, get Steel Developments to recon it.

<hr width=100% size=1>Been there, done that, got the oily T shirt

 

[Dave_Knowles]

Thanks Phil for all your help I am looking forward to giving the new prop a try.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[BarryH]

If you look back at one of your past posts I gave you all the ratios for the drives. As said there a couple of ratios for the petrol one and the ratio for the diesel drive. Have a look on the plate on the transom shield in side the boat. It will have the model number with a suffix letter on yours it;ll be either B or C. The D is the onr for the diesel.

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[Dave_Knowles]

I will have another look. Was unable to find the plate last time I looked but it is not the easiest place to see.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[JOHNPEET]

If you can't get the model No. from the transom shield and the boat is out of the water, you can work out the ratio by putting the drive in gear and rotating the engine crankshaft sufficient revolutions (with a spanner) to turn the prop through 1 revolution you will need somebody else to watch the prop.

I had similar problems with my Birchwood 22 which wouldn't get on the plane.

I had a 145a and 280 drive.

Swapped the 145a last year for a 431 (AQ205) it now does 26 knts at 4600 revs with plenty of throttle left and I still havn't sorted the drive ratio yet - still using the 2.15:1 ratio of my original 280.

So I should better the 26knts eventually

So if anybody knows of a set of gears for the lower unit of a 280b which has a 1.61:1 ratio I would be interested.

John.

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[Dave_Knowles]

26knts I can only dream about. How is the fuel consumption bvecaues with the 151A mine is pretty bad? My boat had the engine replaced in about 1990. What it had before the 151A I don't know but it looks as though the outdrive was not changed.



<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>

 

[duncan]

Dave - I know I made some coment to the effect that I thought you might be underestimating your weight last time - but this time I suspect you have gone the other way!
At 14 knots you are over any resistance hump for that hull, and at 4700 you are well into the engines power band.
Loosing 2-3 inches of pitch should give you 51-5300 and a couple of knots but when you are light (gear, and fuel) you should also see that on the current prop. If you don't then you should be looking at the engine as much as the drive train.

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[Andrew_Fanner]

Is "over the resistance hump for that hull" an "using your skill and judgement"/years of experience thing or is there a mathematical formula for tyros to use, given things like displacement and so forth. While my boat's out I'm reviewing the prop size as I suspect its still wrong.

<hr width=100% size=1>Two beers please, my friend is paying.

 

[Dave_Knowles]

Hi Duncan,

I spoke to Phil last night and he said the same. The boat is quoted as 2,041kg in basic forms so I added the rest to cover fuel, people etc.

<hr width=100% size=1>Dave
Southampton - uk

<A target="_blank" HREF=http://www.MyCleopatra.co.uk>The site for cleopatra boat owners</A>