trim tab advice

[evolution1985]

Hey guys and girls, I need some advice from all you very knowledgeable people on here.
My partner and I just upgraded from my little 1995 bayliner capri 1700ls outboard that I rebuilt to a 1997 wellcraft excell 21sx. We bought this boat fairly cheap with the plans on using it this summer as is and gutting it this winter and rebuilding it as we want it, different seating arrangement, new paint, rebuild the motor, and rewire the boat as there is a little bit of salt water corrosion on the wiring. Now we have had it out nearly every day for the last week since we bought it and it goes like a rocket, it has the 5.7 260hp mercruiser with alpha drive and has plenty of power, but we have found at anything over 25-30mph it becomes very skittish on the water and i believe the term used is "porpoises" all over the place.
It does get worse with less weight in it, and I really don't want to put ballast bags in such as the ones used in wake boats. I have been told that trim tabs or smart tabs would rectify the problem but I am at a loss as to what size ones i should get, trim or smart tabs, I really would like some good advice, and once we begin the tear down i will start a new thread for that.

Cheers Guys and Girls in advance

 

[Bondo]

Re: trim tab advice

Hey guys and girls, I need some advice from all you very knowledgeable people on here.
My partner and I just upgraded from my little 1995 bayliner capri 1700ls outboard that I rebuilt to a 1997 wellcraft excell 21sx. We bought this boat fairly cheap with the plans on using it this summer as is and gutting it this winter and rebuilding it as we want it, different seating arrangement, new paint, rebuild the motor, and rewire the boat as there is a little bit of salt water corrosion on the wiring. Now we have had it out nearly every day for the last week since we bought it and it goes like a rocket, it has the 5.7 260hp mercruiser with alpha drive and has plenty of power, but we have found at anything over 25-30mph it becomes very skittish on the water and i believe the term used is "porpoises" all over the place.
It does get worse with less weight in it, and I really don't want to put ballast bags in such as the ones used in wake boats. I have been told that trim tabs or smart tabs would rectify the problem but I am at a loss as to what size ones i should get, trim or smart tabs, I really would like some good advice, and once we begin the tear down i will start a new thread for that.

Cheers Guys and Girls in advance

Ayuh,.... Are ya changin' the trim,..?? it alone should allow ya to run up to Wot...

How Straight is the last 6' of the hull, just ahead of the transom....
Check it with a straight edge...
A Hook, or Rocker can cause yer Problem...

 

[Philster]

Re: trim tab advice

Middle 90's Wellcraft = risk (actually, a likelihood of water intrusion) and maybe internal rot or soggy structure. The boat could have water in it somewhere that helped bend the hull as it sat on the trailer. If the support structure was weakened and she has a deformed hull, it leads to what Bond-o described.

There is no way a proper Wellcraft hull would porpoise like that and at those speeds. No way.

 

[evolution1985]

Re: trim tab advice

Middle 90's Wellcraft = risk (actually, a likelihood of water intrusion) and maybe internal rot or soggy structure. The boat could have water in it somewhere that helped bend the hull as it sat on the trailer. If the support structure was weakened and she has a deformed hull, it leads to what Bond-o described.

There is no way a proper Wellcraft hull would porpoise like that and at those speeds. No way.

cheers guys for the great heads up. I was paranoid about rot after buying my last boat (1995 bayliner capri 1700ls) which was full of hidden rot. So when i checked the boat, i lifted the carpet in the back corners, checked anywhere where i could see glassed wood, i spent about two hours checking it, im reasonably confident that there isn't much rot, if any. I know that could all change when i gut the boat for the rebuild, and im expecting to find allot where i couldn't check. but the hull is straight there is no deformation, only crazing in the gel coat above the rub rail from the last owner hitting things. I just went out with a straight edge and checked the boat and all is good. i was thinking that it may have had allot to do about the way i was trimming the motor, as i haven't had a 21fter before this. but it isn't all that hard to find the sweet spot as the boat rides allot different when you hit it. it feels like air is getting under the hull and lifting it side to side slightly. so i tried trimming it down but noticed more spray from further up the hull and a reduction in speed.

It is highly likely that im just not used to a boat with this kind of hull in this size as most of the boats ive had or driven were proper wake/ski boats. Hence the question of trim tabs. I have heard of people putting them on bayliner 175's and others of that size with great reviews. anyways any further advice that anyone is prepared to offer Im all ears. any other problem spots to check, or anything else for that matter please pile it on me. Im the first to admit when im wrong and the first to ask for help when not sure so all advice or suggestions are GREATLY appreciated.

 

[evolution1985]

Re: trim tab advice

Ayuh,.... Are ya changin' the trim,..?? it alone should allow ya to run up to Wot...

How Straight is the last 6' of the hull, just ahead of the transom....
Check it with a straight edge...
A Hook, or Rocker can cause yer Problem...

G'day, thanks for the heads up. im pretty certain that im trimming it right? when ive finished trimming, the spray is further to the back of the boat and i get a little jump in speed.

It seems to get to WOT, about 5000 rpm, and hits about 55-60mph (speedo) feels more like 45-50mph but yeah it does run out well and has a bucket load of power and great hole shot, it gets on the plane in only a couple of seconds without a skier or tuber behind.

Oh and its running a standard 19" pitch prop. (alloy)

cheers

 

[evolution1985]

Re: trim tab advice

oh yeah, just went out with the straight edge, absolutely perfect

 

[tpenfield]

Re: trim tab advice

You can trim the outdrive down a tiny bit to take out the porpoising. Trim tabs might help a little bit, but the outdrive is more the thing.

What are we looking at for top speed?

 

[evolution1985]

Re: trim tab advice

You can trim the outdrive down a tiny bit to take out the porpoising. Trim tabs might help a little bit, but the outdrive is more the thing.

What are we looking at for top speed?

i have tried to trim it down and such, but it still feels skittish. top speed is roughly 55-60mph (speedo) but it feels more like 45-50 mph. once i hook up the gps i'll know a more accurate top speed.

 

[chriscraft254]

Re: trim tab advice

Trim tabs and smart tabs are both the same thing. Only diffference is the smart tabs are automatic and the regular trim tabs are manually controlled at the helm. Either will help your boat with adjusting the boats attitude. The smart tabs do it automatically and all you have to do is drive. Check them out on there website, they are particularly good at taking away any porpoising and chine walk. Any trim tabs you chose, you can simply go to there website and get the recommended size or call them. Bennett, lenco nauticus. They all have great service.

Not saying you don't have other issues but the trim tabs are a great addition to any stern driven boat.

 

[evolution1985]

Re: trim tab advice

Trim tabs and smart tabs are both the same thing. Only diffference is the smart tabs are automatic and the regular trim tabs are manually controlled at the helm. Either will help your boat with adjusting the boats attitude. The smart tabs do it automatically and all you have to do is drive. Check them out on there website, they are particularly good at taking away any porpoising and chine walk. Any trim tabs you chose, you can simply go to there website and get the recommended size or call them. Bennett, lenco nauticus. They all have great service.

Not saying you don't have other issues but the trim tabs are a great addition to any stern driven boat.

thanks heaps mate, After hearing what everyone has been saying, and taking it out today, i believe that the problems im getting are not really problems as such, just more me being not used to a stern drive. All the other boats bar, my little bayliner which was an out board have been either vdrive or direct drive wake boats with ballast and wake plates. The main reason I was asking about the trim tabs is a tige I was a driver in had the TAPS system on the back for wake flow. to me it just looked like a large trim tab placed in the middle of the boat, but even that affected how stable the boat was. I honestly did not know what the difference between trim and smart tabs were, i knew that trim tabs were operated at the helm, but i though smart tabs were reasonably fixed? i do appreciate all the help so far from everyone, as its given me new things to consider and new things to learn and check for on my boat.

I am about to look into the smart tab option as I like the idea of auto correcting tabs, sorta fit and forget to a point would be fantastic.