Performance Boat Shop

porpoising problems with my bass boat?

I have an older (1989) bass boat (16.5 ft fiberglass modified V w/ 90 hp outboard). The hole shot takes forever and the boat porpoises like crazy at medium to higher rpms. Also, I haven't opened it up all the way because I just had 2 pistons rebuilt, but it seems like my rpms are higher than they should be (5000 and still not wide open). Without buying trim tabs or a hydrofoil, what other options could I look at to improve performance. Also, I don't know what pitch the prop (black--aluminum?) is, because the stamp is too faint to read. Is there a way to measure the prop to find out what pitch it is?

Public Comments

1. LEARN HOW TO DRIVE
2. You Can decrease the 'tilt angle' of the motor on the transom. This will force the bow of the boat down which helps overcome the leaping or porpoising effects. I know that you state 'without buying trim tabs' but you should reconsider as it will improve your ride and help reduce the hazards of having a 90HP on a 16ft boat. In a 'worst case scenario' You can 'make' your own trim tabs with piano hinges and aluminum plate and a couple of turnbuckles but I really don't advise it unless you are handy at doing this sort of thing. Be careful friend and I hope that you resolve this problem. In this particular case, try reducing the trim angle first, OK? It is your safest bet. About the high RPMs(?); Your boat is most likely 'Cavitating' (catching air) as a result of the leaping/porpoising effect. This will sound as though you are really revving up because the prop cannot stay 100% in the water to engage and reduce the RPM to the correct levels, etc. Trim your boat down as described and I'm most certain the RPMs will come in line with stopping the leaping/porpoising effects! Again, good Luck friend and I do hope this helps. It really should to some extent 'but' if not; please consult a Boat Knowledgeable individual for a better analysis of your particular problem. "There is a solution!"
3. If the hole shot is slow either there is something wrong with the engine as the V4 has a lot of low end power and should rip that boat out of the water. or the prop has to much pitch. And U say u haven't opened up the throttle. Porpoising is cause by 2 thing 1 is the engine trim is to high. Or there is a hook in the hull or a built in hull speed which over 20 MPH it will push the bow down. Most all boats of that vintage had a hull speed built in. It's located 20" from the transom and curves up on the bottom. I have glassed them in flat and the boat will run on the back half of the hull. 5000 is not to high around 5600 to 5800 WOT.Depending on the year.Don't worry about the high end unless U run there all the time. Our new twin 175 HP Suzuki's we run into the rev limiter empty over 6000 RPM and with a load it's 5800.But cruise at 4300 running free.
4. Props have different rake to them as well. Some props have more rake than others which will influence bow or transom lift. Talk to a good prop shop. You'll have the best overall compromise between control and speed with a 4 blade prop.