Speed and proposing problem

[laketroutman]

I have a 2008 Alumacraft Navigator 165CS with a 90hp E-TEC and 13.75x15 aluminum prop. The boat porpoises when I trim the motor up at 35mph. According to alumacraft it should run about 40mph. But when I trim the motor up it starts proposing at about 35mph. The anti-cavation plate on the motor is set level to the bottom of the vee. Would raising the motor up an inch fix the speed and proposing problems?

 

[Moody Blue]

Re: Speed and proposing problem

Porpoising is usually a symptom of a stern heavy boat. Try re distributing some of the weight forward.

My last boat had the same problem. Side console boat with the console at the rear of the boat as opposed to in the middle. Porpoised terribly above 30mph. I installed a set of smart tabs and the problem disappeared. I never would have believed how well they worked, but they did the job very well.

 

[tashasdaddy]

Re: Speed and proposing problem

the best $100 you will spend on your boat. http://forums.iboats.com/showthread.php?t=313041

 

[Capt'n Chris]

Re: Speed and proposing problem

Find your 0 trim angle first and mark it. You will use this reference from now on, so be sure you can see it from the helm. Balance your load properly and make sure you do not have any water in hull. Tabs and tails are generally a band aid when a correct prop most always fixes an attitude problem. If no water is in the hull and the load is balanced right id focus on the prop before resorting to the alternatives. Please fully describe your prop and the max rpms you are hitting with the load you generally carry. We also need to know what the max rpms your motor mfgr specifies.

 

[Jdeagro]

Re: Speed and proposing problem

Capt. Chris;

Why is it that the prop is the focus of small power boat performance issues? The prop should be appropriate for the boat for sure, but it should not be used to address handling issues. It is for propelling.

When you call trim tabs a band aid I find it to be an interesting "handle" for something that significantly improves ride, handling, acceleration, ability to plain, fuel economy, and eliminates porpoising. I would call them a "performance" enhancing device.

For the record, I do not like hydrofoils in general as a slap it on and go item. No news there I guess.

If you think I am making bold claims about trim tabs, I would be happy to provide third party documentation or you can ask the others on the forums.

There are two key ingredients to boat performance; one is the power plant, and the other is the hull design. Both are equally important! Trim tabs adjust the hull design to compensate for the varying conditions. Don't look at only 1/2 of the problem.