Gotcha. My H280"was my first boat and I knew nothing about sailing. Sounds like you have experience....so maybe your knot meter is messed up. A handheld GPS will give you a good idea.
Good luck with your new toy.
Greg
How fast is your H26/260?
- Thread starter rgranger
- Start date
Good luck with your new toy.
Greg
Slow boat speed under power is probably your prop most 9.9 's come with planing props a small heavily pitched prop that work great on a dink but don't push enough water for a displacement hull the best thing to do is take prop off take to repeatable prop shop and trade for power prop they usually will let you keep comming back and tryin another till get it right otherwise your left guessing on internet . one side note if you keep cavitating your prop in water will eventually burn the aluminum or plastic right off
You can google for the PHRF rating for the H260, I don't recall the number. It's not fast but respectable for a little cruiser. I crewed on a H270 last week, it is the same hull you have but with a lead keel. It has a 9.9 outboard that does drag in the water at times. We did see speeds over 6 kts on the GPS without current. We placed 10th out of 14 boats, it was the second race of the season, the captain was happy given our poor start position.
Bob
Bob
Funny you mention the prop.... this one has a four blade prob and it is the only O.B. I've ever had on a sailboat with a four blade prop. I thought it was strange. I'll look into that. It could be I had two things going on and was trying to fit the data to a single variable. The wrong prob and a blown main would both give me slow boat syndrome. I know a O.B. guy who can help me source the prop issue. Thanks for the idea.
Before you mess with the prop and spend $$.. you should verify that you are measuring speed correctly. Crazy to speculate if you suspect your measurement method and it does sound suspect.
Once you know you are measuring speed correctly, get some data on the current prop, then start changing it. On my Mac 26S (also water ballast but lighter) and a 9.8 hp four stroke, I compared a conventional "planning" prop to a high thrust prop measuring both speed and rpm. At low elevation the conventional prop was FASTER than the high thrust prop but at 5000 ft elevation the high thrust prop was faster but in both cases the speed difference was very minor.
Once you know you are measuring speed correctly, get some data on the current prop, then start changing it. On my Mac 26S (also water ballast but lighter) and a 9.8 hp four stroke, I compared a conventional "planning" prop to a high thrust prop measuring both speed and rpm. At low elevation the conventional prop was FASTER than the high thrust prop but at 5000 ft elevation the high thrust prop was faster but in both cases the speed difference was very minor.
I started a thread on this last winter (probably can find it with a search) but I have a three blade "planning" prop and a four blade high thrust prop. In reverse, there is a huge difference between these two props but in forward, you hear "things" on the internet about planning or cavitation for these under 10 hp outboards and the posters never have any actual data.
Keep in mind that the boat speed differences I saw for either prop at wide open throttle were minor - like maybe 4% or so. Both props get you to theoretical hull speed just at slightly different places on the curve. The speed difference in forward is not significant. In the noise compared to the speed issue you are seeing.
What I saw can be explained by torque and rpm (and the outboard rpm rev limiting) which makes sense since power delivered is torque times rpm. At 5000 foot elevation, the outboard will not generate as much power. The high thrust prop is lower pitch so at 5000 ft elevation where the outboard power is reduced, still allowed the outboard to get up into the 5000 to 6000 rpm range. The conventional three blade prop with the reduced hp because of altitude resulted in lower rpm so less delivered hp.
A key thing here also is that a high pitch prop will have higher torque than a low pitch prop at a given rpm (assuming equal blade area as blade area also influences torque).
So at low elevation where the conventional prop resulted in faster boat speed, the conventional prop had an RPM just over 5000. I measured the high thrust prop and it was right at 6000 rpm. Even though the high thrust prop had higher rpm, it is torque * rpm that is the bottom line for power and the conventional prop was simply delivering a higher value for torque * rpm.
Another key thing here is that my outboard has an RPM limiter at 6000 rpm. So for that low elevation case with the high thrust prop, the outboard likely had gone into rev limit. This also indicates that the high thrust prop (5 pitch in this case) had too low of pitch if it allowed the outboard to rev limit.
Keep in mind that the boat speed differences I saw for either prop at wide open throttle were minor - like maybe 4% or so. Both props get you to theoretical hull speed just at slightly different places on the curve. The speed difference in forward is not significant. In the noise compared to the speed issue you are seeing.
What I saw can be explained by torque and rpm (and the outboard rpm rev limiting) which makes sense since power delivered is torque times rpm. At 5000 foot elevation, the outboard will not generate as much power. The high thrust prop is lower pitch so at 5000 ft elevation where the outboard power is reduced, still allowed the outboard to get up into the 5000 to 6000 rpm range. The conventional three blade prop with the reduced hp because of altitude resulted in lower rpm so less delivered hp.
A key thing here also is that a high pitch prop will have higher torque than a low pitch prop at a given rpm (assuming equal blade area as blade area also influences torque).
So at low elevation where the conventional prop resulted in faster boat speed, the conventional prop had an RPM just over 5000. I measured the high thrust prop and it was right at 6000 rpm. Even though the high thrust prop had higher rpm, it is torque * rpm that is the bottom line for power and the conventional prop was simply delivering a higher value for torque * rpm.
Another key thing here is that my outboard has an RPM limiter at 6000 rpm. So for that low elevation case with the high thrust prop, the outboard likely had gone into rev limit. This also indicates that the high thrust prop (5 pitch in this case) had too low of pitch if it allowed the outboard to rev limit.
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