Hi All,
I am hoping that someone on this forum is able to help me.
This spring we bought a 1986 Grew 237, 5.7L 260hp with 4 barrel Quadra-Jet carb and an Alpha 1 (1.47:1 gear) outdrive and a 3 blade propeller for use as a search and rescue boat on Georgian Bay.
I am thinking that I have the wrong propeller on the boat.
Currently WOT is 4600 RPM (so right in the middle of the WOT spec for the engine). However, I can only get about 27 knots on flat water and that is with it trimmed just right according to my GPS. At 3500 RPM, boat cruises at 21.2 knots and if I bring it back to 3200 RPM (the supposed best economy for this engine), it will fall off plane even with the trim tabs.
I have no idea what pitch the propeller that is currently on the boat is as there are no size numbers on the outside of the propeller, and the numbers that are cast on the inside of the hub don't seem to match up to anything on doing an internet search.
I have a friend that has the Grew 230 Scorpion (same hull as mine) and he can cruise at 3200 rpm at 27-30 knots, and pushes over 40 knots at WOT.
I know that my boat is a little heavier as it has the head and small galley in it, but should still be close to the same performance numbers I would figure.
I am wondering if there is anyone that has this same model of boat on the forum that can tell me what they are using for a propeller size and what kind of performance numbers I should expect from the boat. I can't seem to find any information on this on the net.
When I use the calculators on the web for propeller slip, assuming a 19 pitch prop, it shows that it is 44% slip which I figure is way too much and what is causing the sluggishness, but that doesn't explain why I am right in the middle of the RPM WOT range which would suggest the proper pitch? A 21 pitch in the same calculator shows a 48% slip!
I am hoping that someone can point me in the right direction to where I don't have to spend a couple thousand dollars on a selection of props to figure out what I need.
Regards,
Darren
I am hoping that someone on this forum is able to help me.
This spring we bought a 1986 Grew 237, 5.7L 260hp with 4 barrel Quadra-Jet carb and an Alpha 1 (1.47:1 gear) outdrive and a 3 blade propeller for use as a search and rescue boat on Georgian Bay.
I am thinking that I have the wrong propeller on the boat.
Currently WOT is 4600 RPM (so right in the middle of the WOT spec for the engine). However, I can only get about 27 knots on flat water and that is with it trimmed just right according to my GPS. At 3500 RPM, boat cruises at 21.2 knots and if I bring it back to 3200 RPM (the supposed best economy for this engine), it will fall off plane even with the trim tabs.
I have no idea what pitch the propeller that is currently on the boat is as there are no size numbers on the outside of the propeller, and the numbers that are cast on the inside of the hub don't seem to match up to anything on doing an internet search.
I have a friend that has the Grew 230 Scorpion (same hull as mine) and he can cruise at 3200 rpm at 27-30 knots, and pushes over 40 knots at WOT.
I know that my boat is a little heavier as it has the head and small galley in it, but should still be close to the same performance numbers I would figure.
I am wondering if there is anyone that has this same model of boat on the forum that can tell me what they are using for a propeller size and what kind of performance numbers I should expect from the boat. I can't seem to find any information on this on the net.
When I use the calculators on the web for propeller slip, assuming a 19 pitch prop, it shows that it is 44% slip which I figure is way too much and what is causing the sluggishness, but that doesn't explain why I am right in the middle of the RPM WOT range which would suggest the proper pitch? A 21 pitch in the same calculator shows a 48% slip!
I am hoping that someone can point me in the right direction to where I don't have to spend a couple thousand dollars on a selection of props to figure out what I need.
Regards,
Darren