FNQCairns
07-06-2008, 08:58 PM
For anyone who is interested in stuff like this here is part of my journey through proping my boat, it's been delayed by wind and time but most often a lack of interest because most times I put the boat in the water it's to head offshore, not fair on deckies to go testing props when there are fish to catch.
Anyway the pic below are a part selection of props I have,
1st is a vengeance 13 3/8x14p, this prop in standard form works on my boat in offshore trim 2 up and pulls from memory 5550rpm but it is slow! so efficiency at cruise suffers and fuel costs too much now.
2nd is a Yamaha alum 13.5x15p, my engine cannot push this as a standard unmodified prop my small capacity 3cyl 2st 90 yam just doesn't have the torque so I only reach 5200rpm offshore trim 2 up.
Currently on the boat is an identical but backyard modified one which I decreased diameter approx .3 of an inch to finally pull 5650rpm offshore trim 2 up and it now does a good job, much better than the 14p in efficiency.
3rd is a ss yamaha 13.25x17p this is the same prop I ran when I first wet the boat and was trying to beat it's inherent (thanks to a dodgee manufacture) handling problems. http://www.ausfish.com.au/vforum/showthread.php?t=110255&page=2
Last time I ran the SS 17p, because all of the extra weight now in the boat compared to the post in the link I am flat out pulling 4800rpm offshore trim 2 up with this prop.
So I thought about selling it, then I thought why not try and force a way over pitched but ok diameter prop to work on MY boat so the last 2 pics are before the grinder work today and after, it's aggressive and a little rough with a goodly amount of the cup simply cut away which accounts for .5 of an inch pitch (drag) on these props when standard.
Seeing as I talk here about how to get a standard prop working on some individual boats and that reducing diameter makes all of the difference to the hip pocket I thought I would show what I have done today in 30min of work and will add to this what numbers I end up with (good or bad) when I test it, I am hoping that in offshore trim 2 up I can get a wildly 'over pitched for my boat' propeller to a place that extends my cruising range by near 10% -15% over anything I can buy off the shelf and hope that others may try it in the back yard too with a prop that was just as useless to them otherwise.
Props are pretty meat-head in practice on our overweight and overwide fishing boats, it's hard to ruin one for use on any boat but not real hard to ruin one for use on any individual boat.
O yeah, the boat is a pressed 6.2m overall CC approx 850kg in offshore trim, the shape is not unlike the formosa 5.8.
cheers fnq
Anyway the pic below are a part selection of props I have,
1st is a vengeance 13 3/8x14p, this prop in standard form works on my boat in offshore trim 2 up and pulls from memory 5550rpm but it is slow! so efficiency at cruise suffers and fuel costs too much now.
2nd is a Yamaha alum 13.5x15p, my engine cannot push this as a standard unmodified prop my small capacity 3cyl 2st 90 yam just doesn't have the torque so I only reach 5200rpm offshore trim 2 up.
Currently on the boat is an identical but backyard modified one which I decreased diameter approx .3 of an inch to finally pull 5650rpm offshore trim 2 up and it now does a good job, much better than the 14p in efficiency.
3rd is a ss yamaha 13.25x17p this is the same prop I ran when I first wet the boat and was trying to beat it's inherent (thanks to a dodgee manufacture) handling problems. http://www.ausfish.com.au/vforum/showthread.php?t=110255&page=2
Last time I ran the SS 17p, because all of the extra weight now in the boat compared to the post in the link I am flat out pulling 4800rpm offshore trim 2 up with this prop.
So I thought about selling it, then I thought why not try and force a way over pitched but ok diameter prop to work on MY boat so the last 2 pics are before the grinder work today and after, it's aggressive and a little rough with a goodly amount of the cup simply cut away which accounts for .5 of an inch pitch (drag) on these props when standard.
Seeing as I talk here about how to get a standard prop working on some individual boats and that reducing diameter makes all of the difference to the hip pocket I thought I would show what I have done today in 30min of work and will add to this what numbers I end up with (good or bad) when I test it, I am hoping that in offshore trim 2 up I can get a wildly 'over pitched for my boat' propeller to a place that extends my cruising range by near 10% -15% over anything I can buy off the shelf and hope that others may try it in the back yard too with a prop that was just as useless to them otherwise.
Props are pretty meat-head in practice on our overweight and overwide fishing boats, it's hard to ruin one for use on any boat but not real hard to ruin one for use on any individual boat.
O yeah, the boat is a pressed 6.2m overall CC approx 850kg in offshore trim, the shape is not unlike the formosa 5.8.
cheers fnq