I've just got my rebuilt coastworker out on the water for the first time since buying the boat and it was a real pleasure to use, but I'm not getting the engine revving out.
This is the boat - 18' console - similar to whaler I think:
Engine is a 1996 BF75A Honda, and as i understand it the WOT revs should be able to reach 6000rpm.
At full speed on the water I was hitting 34mph on the gps, 2 up, and very light load, at 5200rpm. Couldn't get it to rev higher.
This is with a 19" pitch 3 blade alloy prop, which I thought might be a bit much but only one I have currently.
This was on pretty much flat sea, pretty much perfect conditions for a speed run.
Now of course the obvious thing to do is try a 17" prop if I want the engine to rev higher, but what I'm not sure is if there's really any point or if 5200 is an acceptable WOT rpm?
If I change to a 17" prop, then I would guess the outcome will be I'll get the extra revs and be able to hit 6000RPM, but would then need to use the extra revs to maintain the same speed as before, so maybe still get 34mph, but at WOT and using more fuel I guess as a result?
I understand that if the boat has more people/load then the 17" prop would enable it to get on plane easier and reach WOT at any point, but it's not often I'll have more than 2 up, and I can't help but think that keeping the 19" would give better economy.
Appreciate any input and opinions from prop boffins as I'm not sure what's the best course of action.
Thanks!
There is another factor actually - which is that I'm trying to upgrade the engine to 90 from 75. I think with that extra oomph the 19" prop would then be ok and the engine would be able to rev out, and hit perhaps 37/38mph at 6000rpm. I need to get a 90 carb though as I only have 3 of them currently on my bench.
This is the boat - 18' console - similar to whaler I think:
Engine is a 1996 BF75A Honda, and as i understand it the WOT revs should be able to reach 6000rpm.
At full speed on the water I was hitting 34mph on the gps, 2 up, and very light load, at 5200rpm. Couldn't get it to rev higher.
This is with a 19" pitch 3 blade alloy prop, which I thought might be a bit much but only one I have currently.
This was on pretty much flat sea, pretty much perfect conditions for a speed run.
Now of course the obvious thing to do is try a 17" prop if I want the engine to rev higher, but what I'm not sure is if there's really any point or if 5200 is an acceptable WOT rpm?
If I change to a 17" prop, then I would guess the outcome will be I'll get the extra revs and be able to hit 6000RPM, but would then need to use the extra revs to maintain the same speed as before, so maybe still get 34mph, but at WOT and using more fuel I guess as a result?
I understand that if the boat has more people/load then the 17" prop would enable it to get on plane easier and reach WOT at any point, but it's not often I'll have more than 2 up, and I can't help but think that keeping the 19" would give better economy.
Appreciate any input and opinions from prop boffins as I'm not sure what's the best course of action.
Thanks!
There is another factor actually - which is that I'm trying to upgrade the engine to 90 from 75. I think with that extra oomph the 19" prop would then be ok and the engine would be able to rev out, and hit perhaps 37/38mph at 6000rpm. I need to get a 90 carb though as I only have 3 of them currently on my bench.