How much pitch to drop??

[96720]

I’m totally confused after doing a test run of my rebuild it’s 16’ x 6.5’ semi-v hull weight is estimated at about 1500lbs with twin 30hp Hondas. The engines have stock 9.25”x12” props fitted. I’m unable to reach anything near the 5,000 to 6,000 rpm WOT range listed by Honda. Here are some random rpm and speed values that I was able to get, 1900rpm/21mph, 2200rpm/21mph and 3800rpm/26mph (mph was taken on GPS). 3800 was the highest rpm I was able to obtain at about ¾ throttle because of other issues (porpoising, which I need to resolve).

In order for me to achieve the proper rpm range how many inches of pitch do I need to go down? Honda has props from 8” to 11” in pitch. Which would be the best choice for me to start with? Any input would be greatly appreciated.

 

[SkiDad]

don't drop any. I'm not quick to say a tach is off but yours is WAY off - you have a 2.08 gear ratio - so at 26 mph you are at 5300 rpm at 10% slip or 5500 at 13% slip. It hard to say but you at at least in the range. You are good and your speed is good as well - you need to check your tach is set on 3 cylinder mode or something like that.

 

[steelespike]

Seconded; Tach appears way off.

 

[Sea Rider]

See no point having 30 HP twins at back tramsom, although you have 60 HP (double torque to move more load) will not outperform or even equal top speed of a single 60 HP engine. Personally would get rid of those twins and go for a single 60 or one near max transom rated engine for that boat. Twins are double headache when parts, maintenance services are required.

Happy Boating

 

[Texasmark]

You can't control your porpoising with your trim settings?

 

[96720]

don't drop any. I'm not quick to say a tach is off but yours is WAY off - you have a 2.08 gear ratio - so at 26 mph you are at 5300 rpm at 10% slip or 5500 at 13% slip. It hard to say but you at at least in the range. You are good and your speed is good as well - you need to check your tach is set on 3 cylinder mode or something like that.

Yeah, I was rather confused with the rpm and the speed that I was getting. Plus both tachs were reading the same. At idle it's where its supposed to be but something gets messed up when throttling up. Thought it was odd I'll check the settings again.

 

[96720]

See no point having 30 HP twins at back tramsom, although you have 60 HP (double torque to move more load) will not outperform or even equal top speed of a single 60 HP engine. Personally would get rid of those twins and go for a single 60 or one near max transom rated engine for that boat. Twins are double headache when parts, maintenance services are required.

Happy Boating

Thanks for the suggestion. I'm not really into the speed thing. A single would be good but in the past coming home with a kicker just doesn't make it where I boat.

 

[96720]

You can't control your porpoising with your trim settings?

Tried moving weight forward and different trim settings both didn't work. At the current time it seems as though 23-24 mph is the borderline.

 

[96720]

don't drop any. I'm not quick to say a tach is off but yours is WAY off - you have a 2.08 gear ratio - so at 26 mph you are at 5300 rpm at 10% slip or 5500 at 13% slip. It hard to say but you at at least in the range. You are good and your speed is good as well - you need to check your tach is set on 3 cylinder mode or something like that.

Thanks so much. Checked the tach yesterday it was set on the wrong poles P-4 instead of P-2. Hope I have a chance to give it a run this weekend. Really hope Tropical Storm/Hurricane Ana doesn't screw up my plans!

 

[Watermann]

Try out a set of Nauticus smart tabs, they are incredible and I bet the porpoising problems become a thing of the past. Your problem lies in the added weight of those twins that you can't overcome with the trim. I would suggest the 60# model and factory blemish one here at iboats are priced right at 100 bucks.

 

[old islander]

+1 on the smart tabs. Your probably a little tail heavy with the twins. The smart tabs will apply lift to the transom while your running. Don't be supprised if your top speed goes up slightly as well as your MPG. When I added them to my Sea Ray, it was the best single improvement I made to the boat. It gets on plane at half the speed it used to take.