Re: Smart Tabs - Nautijohn
Ckone;
I am flattered that you asked me to jump in here (from another post), and I would like to tell you that the performance issue is simply the need for trim tabs. However, after reading all of the postings, I go back to the Yamaha test of a similar boat that had very different results. It does not sound like the HP to weight ratio is the problem either, not that it wouldn't do a bit better with more HP, but your problem is bigger. It sounds like you are not getting enough HP to the prop. It could be that the prop is incorrect (which may not be the issue either since the Yamaha test was with the same prop.
The simple test would be to try a different prop, the same as used in the Yamaha test. This will tell you quickly if the prop is OK, and will tell you in a few seconds of operation. If the performance mimics the Yamaha test then your in business. If changing the prop does not produce any better results then you have an engine issue. I am not going to recommend a larger engine as this does not address the problem with the engine you have, and it could be very satisfactory if running correctly. I am also assuming that the weight of the boat is similar (within a few hundred lbs.)
Remember that stepping up from a 115 HP to a 150 HP does not give you the extra 35 HP where you need it (at 2500 RPMs) since the additional HP is only developed completely at the higher RPM range (about 5500 RPMs). You will only get about 15 to 17 HP to use when trying to get on plane. Your problem is bigger than that. And my guess is that you could make that boat plane with a 90 HP, although it would be a strain.
Process of elimination (in order of priority and simplicity):
1) Try a different prop of the same size as used in the Yamaha test.
2) Get the engine checked by the Yamaha authorized Dealer, and Call the factory to involve a tech representative if necessary.
Once the problem is identified then move forward to fine tuning the performance.
There is no doubt that trim tabs (Smart Tabs or helm controlled Tabs) will improve the performance, ride , handling etc, but lets not hide the problem. Fix it first, then make it even better!
