porposing help

[quikstang347]

i have a nice 79 mako 21 it has an Evinrude Ocean Pro 175 the problem is i am having issues with the thing porpoising it takes a long time to plane maybe 8-12 seconds. once on plane it runs great except for when i hit a small wave maybe 2-3 ft it starts to bounce and will eventually settle down just to with the next. it is not a consistant ride. it has trim tabs that are non functional . i did put a hydro stabilizer on the lower of the engine and it helped tremendouly but is not corrected. if i lower the trim tabs manually and hose clamp them in place once i get it right so it doesnt lisp either way it runs great and no issues , but it kills my speed. there has to be something here i can do or i am not doing correctly. this is the first classic mako i have owned and always owned new boats prior. i do have the longstaft i believe 30" shaft motor and the cavitation plate is even with the bottom of the hull . i had several people look at it and everyone agrees that the motor is installed correctly. my question is where sould i look and what should i do . are these boats meant to only run with trim tabs down. thanks for any help in advance

 

[capt sam]

Re: porposing help

fix the trim tabs and are you trimming the motor at all?

 

[quikstang347]

Re: porposing help

i have to keep the trim all the way down. if i lift it it gets worse. i am planning on taking the stabilizer off the motor and using the tabs tomorrow and see how that goes .

 

[capt sam]

Re: porposing help

the fin will really change the handling characteristics. That boat shouldn't porpise that bad.

 

[quikstang347]

Re: porposing help

yeah it is a bear to steer now even with hydraulic steering. never was like that i am taking that damn thing off first thing tomorrow, i will clamp the trim tabs with a lot of careful measuring and test it if it works like i hope i will go buy new tabs, thanks for all the help.

 

[QC]

Re: porposing help

Get rid of the tail, fix the tabs . . . problem solved Also shift any weight you can forward. Porpoising is primarily due to balance, too little forward . . .

 

[Willyclay]

Re: porposing help

Any chance your 30 year old boat has water-logged floatation foam? The additional weight could be affecting the handling. Good luck!

 

[quikstang347]

Re: porposing help

i thought of that and checked the coufin area where the tank goes as well as the transome . it is dry as a bone. it was out of the water for 8 months in the heat put it back in and did the same thing. i contribute it to the tabs, and maybe underpower. i will try to make some adjustments tomorrow and see what happens

 

[woosterken]

Re: porposing help

here is a good read for ya.
http://www.clubmarine.com.au/internet/clubmarine.nsf/docs/MG19-2+Technical

hope it helps

woosterken

 

[quikstang347]

Re: porposing help

since this has always been like this i wonder if the motor is mounted to low. the cavation plate is abou 2" below the keel (lowest point) do you think that if i raise it 1" above the keel it would help. that is the only thing i have not tried

 

[ondarvr]

Re: porposing help

At first you said the A/V plate was even with the keel, now you say its 2" lower, plus the tabs don't work. Fix these two things and probably 90% of the problem will be fixed, that is if the foam is dry like you said.

 

[capt sam]

Re: porposing help

yeah that 2" can make a big difference and there's no real way to clamp those tabs to work, they need to be down to get on plane and up to run at speed. Raise the motor and fix the tabs.

 

[steelespike]

Re: porposing help

If your not having any ventilation(cavitation) problems the motor is probably too low. Raise it to a point just before venting becomes a problem.Prop selection may help your problem and help improve motor height.

 

[NSBCraig]

Re: porposing help

You know if you can't afford to fix your tabs you can retro them to automatic smart tabs.

iboats sells the kit.

http://www.iboats.com/Nauticus_Smar...4940219--**********.652513059--view_id.237885

 

[180shabah]

Re: porposing help

Have you checked the hull?
Put a straight edge against it, starting at the transom running forward. Do this two or three places between the keel and chine on each side.

If the running surface isn't flat, it can cause some handling problems.

 

[Nandy]

Re: porposing help

Your boat is not supposed to behave like that.... If your foam is waterlogged you wont necessarily be able to see it. Sometimes it take to cut a hole from top to bottom in the foam to see the waterlogged foam. You could also weight it in a truck scale and compare the weight to what it is supposed to be. Your motor being that low will have an impact, but to me it sounds like you might have extra weight somewhere, whatever is your setup or waterlogged foam.
Start with setting up the motor as you been told. Doelfins mostly helps small boats, your boat will be helped better with tabs.
Good luck.