seafox67
Well-Known Member
The engine has only just done 20 hours. Would this be enough to block the exhaust?
I hacked 1.5 inches off my prop!!
- Thread starter seafox67
- Start date
The engine has only just done 20 hours. Would this be enough to block the exhaust?
Tranona
Well-Known Member
No. It revs to 3200. The earlier 20X0 did max at 3600.
fisherman
Well-Known Member
NorthUp
Well-Known Member
www.falpropellers.co.uk are the best in western Europe. No connection, just experience ☺
PetiteFleur
Well-Known Member
Interesting - I'd forgotten that on my previous boat, a Jaguar 27, when I went for a trial sail the owner said he never went over 2500rpm, but when I got the boat the engine wouldn't go above 2500rpm! On investigation I discovered that a small inline fuel filter had been fitted which was totally gunked up - when removed the engine went to 3600rpm under load. A good and cheap result.
lw395
Well-Known Member
I could be completely wrong on this, but isn't the 2.63:1 figure for going astern?
Is it not 1.95 in forwards?
It would help a little if the prop was smooth.
Here is another calculator.
https://www.vicprop.com/displacement_size.php
I guessed 8ft for the waterline beam and 1ft for the draft excluding keel.
This suggested 6.3knots with 18HP
Is it not 1.95 in forwards?
It would help a little if the prop was smooth.
Here is another calculator.
https://www.vicprop.com/displacement_size.php
I guessed 8ft for the waterline beam and 1ft for the draft excluding keel.
This suggested 6.3knots with 18HP
seafox67
Well-Known Member
Not sure... the label on the gearbox says 2.63 so I'm assuming that is for forward and backwards
seafox67
Well-Known Member
Thanks for the feedback... It's definitely worth la closer look. I had assumed the original fuel system would have had a service during the engine install...
but, then you can't take anything for granted in the wonderful world of boats
seafox67
Well-Known Member
Yes, Mark was very helpful. Unfortunately, the prop would of needed to go into the machine shop to sort out the taper and the delay was too long for this time of year. Maybe look at FAL again in the winter when the boat comes out again.
fisherman
Well-Known Member
Don't know if the calc method has been put forward, but simply: pitch indicates the distance forward in inches a prop would move in one revolution, through butter, then allow 30% slip to get to hull speed for that HP. But if you ring C&O engineering with boat and engine spec they will tell you the prop you need. I suppose you could possibly then go to Woods for a used one, no real reason not to. Or if you have a standard production boat you could look at some others.
seafox67
Well-Known Member
Yesterday, with my custom/hacked down prop. I tied the boat securely to the pontoon and put the engine into full forward. I usually get 2000 rpm at full forward throttle. I got 1500 rpm which I expected considering the boat is being held back by the pontoon.
However, when I put the boat in full reverse, I got 2600 rpm
My gearbox is a MS15A-B. Does this mean I have a different gear ratio for reverse? (2.63 for forward and 1.95 in reverse)
lw395
Well-Known Member
Yesterday, with my custom/hacked down prop. I tied the boat securely to the pontoon and put the engine into full forward. I usually get 2000 rpm at full forward throttle. I got 1500 rpm which I expected considering the boat is being held back by the pontoon.
However, when I put the boat in full reverse, I got 2600 rpm
My gearbox is a MS15A-B. Does this mean I have a different gear ratio for reverse? (2.63 for forward and 1.95 in reverse)
Other way around more like.
Engine RPM 2.63x prop RPM in astern,
Enigine RPM 1.95 (?) x prop RPM in rwd.
seafox67
Well-Known Member
This is getting very interesting!
I found some official specs on my gearbox. The label on my gearbox says 2.63. The specs say RH Ratio 2.63:1 and LH Ratio 1.95:1.
My prop travels in a left hand direction.
So does that mean when my prop is pushing the boat forward and turning in a left hand direction (it is a left hand prop) my gear ratio is 1.95?
This might then explain why prop works better in reverse because it would be using 2.63 ratio. Which is what I have used to calculate the prop size!
I would be very grateful for any feedback or opinions as I may need to recalculate the prop size for my new propeller later this year.
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neil1967
Well-Known Member
But the gearbox reduces the speed of the prop, so at 1000 RPM (engine), 1.95 ratio gives a prop rotation. of around 500 RPM and 2.63 would give 380 RPM
seafox67
Well-Known Member
That's my concern... I'm starting to think the gearbox is using 1.95 to go forward when it should be 2.63. The rotation feels like it is going to fast for the prop in forward motion but is fine in reverse.
I calculated the prop size for 2.63 (which is what the boat should to using in forward motion) which is about 17".
vas
Well-Known Member
sorry, not quite my field, but don't you think that you simply did the wrong calc by using 2.63 whereas you should have calculated the prop size with 1.95 ratio?
that or change to a RH prop of the said dimensions and swap the gear cable around
probably chop another 3inch off the prop and see how it goes fwd? but then you'll end up with a scrap prop, or even worse a wind assisted only boat...
cheers
V.
seafox67
Well-Known Member
sorry, not quite my field, but don't you think that you simply did the wrong calc by using 2.63 whereas you should have calculated the prop size with 1.95 ratio?
that or change to a RH prop of the said dimensions and swap the gear cable around
probably chop another 3inch off the prop and see how it goes fwd? but then you'll end up with a scrap prop, or even worse a wind assisted only boat...
cheers
V.
I'm sure that I should be using 2.63 as the label on the gearbox only says this gear ratio;
I can live with what I have now but my worry is when I come to buy the new prop later this year. I don't want to give out the wrong information to the prop supplier.
If I need a RH prop, then that's fine.
Is there an easy visual way to see which gear ratio has been selected when I move the control lever forward?
I certainly don't want to be driving in reverse for the rest of my life
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vas
Well-Known Member
hm, it's complicated, have a look at this looks like they've been there and know (?) what they're saying...
http://www.cruisersforum.com/forums...can-i-use-any-of-them-to-go-ahead-110097.html
cheers
V.
http://www.cruisersforum.com/forums...can-i-use-any-of-them-to-go-ahead-110097.html
cheers
V.
lw395
Well-Known Member
Surely Volvo or a dealer could clarify?
fisherman
Well-Known Member
PRM boxes run happily either way, but the emergency 'get you home' will be astern if rigged backwards (as one chap found, he did 16nm astern all the way.)