Harbor Master 19

[fishingdan]

A+++++ for Uncle Ralph. Fantastic job.

[UncleRalph]

THanks for all the compliments guys.

How did she behave herself on the water?

I need to qualify my answer with the fact that this is the first power boat I have owned. I have driven a few power boats, but never owned one. It seemed to handle quite well. I had hoped for a couple of more mph's, but it is a brand new motor. There did not seem to be a very abrupt transition from displacement to planing - it just seemed to gradually pick up speed. The water was pretty calm, maybe a 4-6 inch chop. A couple of times crossing the wake of other boats, the prop seemed to cavitate. I don't know if this is normal or not. The cavitation plate is set up almost exactly at the bottom of the hull.

Ralph

[Rick]

I had hoped for a couple of more mph's, but it is a brand new motor. There did not seem to be a very abrupt transition from displacement to planing - it just seemed to gradually pick up speed.

Ralph, you are this close to experimenting with your prop. I've seen this before...

[Toni V]

Beautiful boat! Congratulations!

Quite strange with the performance. What pitch is the propeller?

You are running the engine a bit too high revs, not much though. The engine would be happier with little lower rpm's.

There seems to be some oddities - like the fact that it sounds the prop is getting air in waves. Also the speed numbers indicate that the prop slips more than it should - prop might get little air all the time. you could try to install the motor lower, the boat's skeg might change the ideal motor depth. Try different trims on engine - maybe it's trying to push bow too deep now.

If you think all is running well, then you could try a prop with 2" more pitch. But I would test a bit more with your current prop.

[JohnH]

Ralph,

Back in October on this same thread, you mention you took it to the boat shop to have the motor installed. Did they set the motor up for you with regard to the prop, pitch skeg etc.? Or did they just mount it on and wish you luck? I would have thought that they should have had some experience at judging the best set up for your boat and the Honda.

Regards
John H

[fishsalmon]

I would agree with Tony, look at the pitch of the prop. I do not like my engine to turn more than 5800-6000 RPM. I would consider re-pitching the prop to avoid exceeding 6000 RPM. It will give it more bite and though you may not accelerate (hole shot) as quickly you should see a better top end speed. Blake

[UncleRalph]

Thanks for all the prop advice. The dealer that installed the motor did put it in the water to test the prop. They told me it maxed out at 5800 rpm. I am not exactly sure how I got it to 6200 rpm. The Owners Manual says maximum should be 5500 - 6000. I probably will try a different pitch in the spring (the current prop is a 13 inch pitch). Unfortunately the motor is as low as it can go without cutting down the transom - not something I want to try just yet.

The skeg may be having an effect, although it is pretty small, about 3/4" by 3/4". In a thread not to long ago I think Jacques said he didn't think a small skeg should have much impact at slower speeds, meaning, I think, less than 35 or 40 mph.

For all you knowledgeable prop guys - what effect does switching from aluminum to stainless steel have?

[jacquesmm]

If you get 6200 rpm (too much), it indicates that you could use more pitch.
13" pitch isn't much. Looks more like a pontoon boat prop. What's the diameter?
You can also cup the prop but I would try more pitch.
An SS prop will give you sligthly better performance at equal rpm because it doesn't flex but I think you don't have enough pitch.
PS: I am not an outboard expert. I can calculate a basic outboard prop but I am not as knowledgeable as some of our builders. Correct me if am wrong. about the pitch.

[UncleRalph]

If you get 6200 rpm (too much), it indicates that you could use more pitch.
13" pitch isn't much. Looks more like a pontoon boat prop. What's the diameter?

The diameter is 11-1/8". It is one of Honda's standard props.

I'm going to try to take it out again in the next few days. If I still get 6200 rpm I will take the prop back to the dealer and see if I can exchange it for one with more pitch.

Ralph

[Toni V]

I thought about 13" pitch.

So, let's calculate; 6200 rpm (engine), gear ratio 2,08 (from Honda's website), 13" pitch.

The calculation gives 36,7 mph speed. (6200rpm/2,08*13 inch=38750 inch/min= 36,7 mph). In reality the propeller will slip in the water and the speed will be lower than calculated there. The slip in this case would be 37% (because you measured 23 mph). And this figure is not what usual planing boat should have. Most planing boats have slip around 5-15%. Like couple people here in the forum has had 7-8% slip which is very typical. The high slip value is what I'm wondering about. Of course it can be okay, it's just more than I've seen in the some cases I've been studying. That's why I would try some different setups trim angles etc. to make sure the prop is not getting air.

Also did you check the speed measurement?

If all is right the and you'll change to different propeller (assuming same slip and speed)
14" will give 5750 rpm
15" will give 5400 rpm.

Note that as the rpm's drop the motor will generate more power (max power at 5750 rpm), so 14" should give slightly higher speed and rpm's as mentioned above.

The Honda engine is running quite high rpm's naturally. But if you can change the prop select atleast 14" most likely the 15" would be best (atleast if you don't run occasionally with heavy loads).

You could cup the propeller too, it might get better. But I guess it's easier to change the prop if you can do it without charge.