is motor installed correctly? have porpoising problem at higher rpms

[jestor68]

Re: is motor installed correctly? have porpoising problem at higher rpms

Problem solved. You can believe, or not.

Or, as suggested earlier, you can go to the nearest garden center and get a couple of 50 lb bags of play sand and place them as far forward as possible in the bow area. That should be enough to shift the CG forward sufficiently to stop the porpoising.

 

[V153]

Re: is motor installed correctly? have porpoising problem at higher rpms

Center motor on transom. Set height so cav plate is 3/4" above keel. Find right prop. In the event of porpoising increase speed and/or trim down.

Do NOT waste your money on 'attatchments' that may or may not work. Perish the thought but mebbe there's a problem with the hull?

-

 

[beardeddone]

Re: is motor installed correctly? have porpoising problem at higher rpms

View attachment 175771 Problem solved. You can believe, or not.

I tend to agree and a lot cheaper then smart tabs and for me it worked, I wished I still had this boat, all well..

 

[Charlie in TX]

Re: is motor installed correctly? have porpoising problem at higher rpms

Smart Tabs. The anti-vent plate wing did not work for me. With Smart Tabs the boat will 'rise' out of the water onto plane staying level. Before ST it would raise bow, plow a little while gaining speed, then role onto plane. Plus it ended the porpoising that the wing did not.

 

[greenbush future]

Re: is motor installed correctly? have porpoising problem at higher rpms

That wing that fixes problems sure isn't good for your lower unit, and it is also masking another problem. Band aids like that can work but my guess is you have a very small flaw (hook some call it) on your hull. Could be so small that you wont see it without a straight edge. Lay a 4 foot level on your hull (Bow to stern) both sides of the outboard. If this is a alum. hull you can usually bang this gap out with a block of wood inside the boat. I've seen a 1/8 inch gap cause this problem before. It's called tuning you hull, and not too uncommon in tin boats.
I would start with this, and see if you can avoid the stuff (fins and tabs)that this boat should never need to begin with. If you still have a problem, I'd consider getting that wedge out of there, that too is a new one that I have never seen.

 

[Outsider]

Re: is motor installed correctly? have porpoising problem at higher rpms

commonly refered to as a hook in the hull.

The wedge is the clue that the problem may be in the hull. First, get the motor centered on the transom and plumb with the transom, with or without wedge. All the add-on crap is a band-aid, get the other stuff 'right' then decide on the size of any band-aid needed .

 

[Black as]

Re: is motor installed correctly? have porpoising problem at higher rpms

Have a look at this link Trim Tabs: Smart Tabs it may sort out your problem

 

[cyclops2]

Re: is motor installed correctly? have porpoising problem at higher rpms

O K

First motor was junk. Ran level.

Second motor is better. Nothing else changed. Runs crummy. Give me a break.

Compare the size & locations of the cavity plates on both engines.
ACTUALLY weigh the engines. 50 pounds added on the transom is a LOT. Need to add counter weight to the bow area.
Small piece of old railroad track, bags of stone uner floor boards........plastic bags only

 

[ufm82]

Re: is motor installed correctly? have porpoising problem at higher rpms

Yes, rearrange the weight in the boat if possible.
NO do no add weight to the boat. (Is it only me that thinks this is counterproductive???)
NO do not spend money on a foil or even Smart Tabs (although I do recommend the Smart Tabs in the right situation)
NO I do not think you have a hook that is causing your issue
NO the engine is not too high- Having the anti-ventilation plate 3/4" above the keel is fine
Lowering the motor may help because the increased drag may slow you down to the point that the bow lift issue becomes moot

IMHO the way to fix this issue with this boat is to look at a prop swap. You don't list an WOT number or a speed currently but I'd love to know what they are. I'd bet you have a plain aluminum prop with zero cup currently. And possibly too low a pitch. That would be my first place to look for a fix here.

The other thing to remember is that you simply don't have enough horsepower to run at full throttle and hold the bow up. You should be able to trim up to the point where the poroising just starts and then back off a bit. That will be your top speed. I can't tell by the picture- does this engine have trim and tilt or is it in fact a manual trim set-up? My 50hp Johnson had T&T and it looked much the same under the bracket. If it is T&T how far up are you trying to trim?

What did the Nissan come off of? Another aluminum boat? Johnboat or V-hull. Or worse, a pontoon even? My suspicion is the prop. I've found that tabs, foils and other "secondary" fixes do not give you the results need if the basic set-up parameters are not met. You don't want to run a 4:10 gear in a highway runner or a 2.72 gear in a strip car. You gotta get the basic drivetrain right before you start adding accessories.

 

[cyclops2]

Re: is motor installed correctly? have porpoising problem at higher rpms

Small Aluminum boats 16' +- a foot can be touchy to stern weights.
My 16' CHEAP 15" short shaft hull with a Evinrude electric start 9.9 hp,6 gallon tank in transom, size 24 deep cycle battery in transom, 10 pound anchor in transom, me on the rearmost seat IS STERN HEAVY. WOT & strong headwind WILL BLOW IT OVER.
I have a 10# anchor & electric winch in bow, 100' of 1/2" line, 20# of assorted junk up there.......It WILL porpose if the motor is NOT TUCKED IN ALL THE WAY.

Cure is a person in the front seat or riding on the bow.........Very safe ???

Lets get real about the problems when motors are changed.

My boat CAN NOT EVEN PLANE !!!!!!!! SO is transom weight very critical or positioning passengers ???????????

Yes

 

[dan02gt]

Re: is motor installed correctly? have porpoising problem at higher rpms

Yes, rearrange the weight in the boat if possible.
NO do no add weight to the boat. (Is it only me that thinks this is counterproductive???)
NO do not spend money on a foil or even Smart Tabs (although I do recommend the Smart Tabs in the right situation)
NO I do not think you have a hook that is causing your issue
NO the engine is not too high- Having the anti-ventilation plate 3/4" above the keel is fine
Lowering the motor may help because the increased drag may slow you down to the point that the bow lift issue becomes moot

IMHO the way to fix this issue with this boat is to look at a prop swap. You don't list an WOT number or a speed currently but I'd love to know what they are. I'd bet you have a plain aluminum prop with zero cup currently. And possibly too low a pitch. That would be my first place to look for a fix here.

The other thing to remember is that you simply don't have enough horsepower to run at full throttle and hold the bow up. You should be able to trim up to the point where the poroising just starts and then back off a bit. That will be your top speed. I can't tell by the picture- does this engine have trim and tilt or is it in fact a manual trim set-up? My 50hp Johnson had T&T and it looked much the same under the bracket. If it is T&T how far up are you trying to trim?

What did the Nissan come off of? Another aluminum boat? Johnboat or V-hull. Or worse, a pontoon even? My suspicion is the prop. I've found that tabs, foils and other "secondary" fixes do not give you the results need if the basic set-up parameters are not met. You don't want to run a 4:10 gear in a highway runner or a 2.72 gear in a strip car. You gotta get the basic drivetrain right before you start adding accessories.

Good advice here! Porpoising can be caused by the motor trying to lift the bow but if the prop can't take the load because of no cup or not enough blade area it slips and causes the bow to fall. Check out your prop situation and motor height before adding anything.

 

[cyclops2]

Re: is motor installed correctly? have porpoising problem at higher rpms

Well we do not know the age Of the original motor. Shaft horsepower ? Lab rated horsepower ? weight of the engine ?

Is the new engine much heavier & propshaft higher horsepower ? I see tons of boats throwing rooster tails with surging engine rpms.
Trimout even more. Looks & sounds super duper racy.
2 types of porposing to me,
Bow is bobbing up & down
Bow is bobbing up & down with engine surging.

 

[smokeonthewater]

Re: is motor installed correctly? have porpoising problem at higher rpms

Let's just settle this ONCE AND FOR ALL! I'll offer a bounty of $5 billion dollars (no not really) for anyone who has ACTUALLY TRIED smart tabs on ANY boat who doesn't believe wholeheartedly that they will make a night and day difference on the O/P's boat and make the porpoising problem instantly disappear.

Further I'll offer a $10 million (again not really paying lol) for ANYONE who ever tried smart tabs and took them off in favor of an add on foil for the lower unit.

Please note the below smiley which according to internet protocol means that this post however pointed is in fun and you aren't allowed to get mad OR sue me for millions of dollars! lol

:laugh:

 

[jestor68]

Re: is motor installed correctly? have porpoising problem at higher rpms

The mention of "smart tabs" always makes me smile. :laugh:

 

[cyclops2]

Re: is motor installed correctly? have porpoising problem at higher rpms

All the other butt raisers are not smart.

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

O K

First motor was junk. Ran level.

Second motor is better. Nothing else changed. Runs crummy. Give me a break.

Compare the size & locations of the cavity plates on both engines.
ACTUALLY weigh the engines. 50 pounds added on the transom is a LOT. Need to add counter weight to the bow area.
Small piece of old railroad track, bags of stone uner floor boards........plastic bags only

1st i never said 1st motor was junk,,nor did i EVER say 2nd motor was better and it still runs crummy...this boat was set up like this when i got it....my nissan runs perfect...its the boat that is having the issue...

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

Yes, rearrange the weight in the boat if possible.
NO do no add weight to the boat. (Is it only me that thinks this is counterproductive???)
NO do not spend money on a foil or even Smart Tabs (although I do recommend the Smart Tabs in the right situation)
NO I do not think you have a hook that is causing your issue
NO the engine is not too high- Having the anti-ventilation plate 3/4" above the keel is fine
Lowering the motor may help because the increased drag may slow you down to the point that the bow lift issue becomes moot

IMHO the way to fix this issue with this boat is to look at a prop swap. You don't list an WOT number or a speed currently but I'd love to know what they are. I'd bet you have a plain aluminum prop with zero cup currently. And possibly too low a pitch. That would be my first place to look for a fix here.

The other thing to remember is that you simply don't have enough horsepower to run at full throttle and hold the bow up. You should be able to trim up to the point where the poroising just starts and then back off a bit. That will be your top speed. I can't tell by the picture- does this engine have trim and tilt or is it in fact a manual trim set-up? My 50hp Johnson had T&T and it looked much the same under the bracket. If it is T&T how far up are you trying to trim?

What did the Nissan come off of? Another aluminum boat? Johnboat or V-hull. Or worse, a pontoon even? My suspicion is the prop. I've found that tabs, foils and other "secondary" fixes do not give you the results need if the basic set-up parameters are not met. You don't want to run a 4:10 gear in a highway runner or a 2.72 gear in a strip car. You gotta get the basic drivetrain right before you start adding accessories.

it maybe the prop i dont know...as far as motor goes,,,it was like this when i bought it...there are no local nissan dealers around here, so what this motor came off of is anyones guess. i do know that the prop is just the standard white looking factory type prop..its aluminum and there are no bends or nicks on it whatso ever...i checked the hours on the motor and its very low... the motor is an 05 model with less than 100 hours on it.. i will check prop size tonight and look into changing it,,, the trim set up is on the throttle handle. thumb controlled..

 

[beardeddone]

Re: is motor installed correctly? have porpoising problem at higher rpms

1st i never said 1st motor was junk,,nor did i EVER say 2nd motor was better and it still runs crummy...this boat was set up like this when i got it....my nissan runs perfect...its the boat that is having the issue...

I certainly am no expert on any of this as far as smart tabs or hydrofoils go, all I can say is when I had that boat it ran and planed great for several months, then all of a sudden one day it started porpoising for no apparent reason I could see, someone at the ramp said to try a hydrofoil stabilizer and I looked at several even on various boats and decided to try one and it did work out great for me, I never remembering seeing any boat using smart tabs or anything like it then, no more problems with porpoising, maybe it's me, but I can't see how it would hurt the lower end, maybe if the transom if it was weak this could be a problem there, but at this point I don't care about that and am not going to address this anymore as everyone has there opinion right or wrong, who knows and we know how many that there is, but the one thing after looking at your setup again interests me, looking at the trim pin, when your at WOT and on on plane is your motor being stopped from going down or in from that pin, just wondering if your motor is being allowed to go down or in far enough, I know it should be able to with that wedge in there, but without seeing this in action I can only guess, hard to tell..

From what I can interpret here in this forum there are many variables on how any of this can be done for improving anything a person wants to do on his or her boat and what works for me may not work for you and visaversa and do try to take all advise here at face value as there are plenty of been there people on here and I respect their input as I will never be able to learn it all and in most cases don't want to, I just try to keep a perspective and am glad we have this information available to all of us to enjoy and pass the time with..

The main this is to enjoy your boating experience

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

I certainly am no expert on any of this as far as smart tabs or hydrofoils go, all I can say is when I had that boat it ran and planed great for several months, then all of a sudden one day it started porpoising for no apparent reason I could see, someone at the ramp said to try a hydrofoil stabilizer and I looked at several even on various boats and decided to try one and it did work out great for me, I never remembering seeing any boat using smart tabs or anything like it then, no more problems with porpoising, maybe it's me, but I can't see how it would hurt the lower end, maybe if the transom if it was weak this could be a problem there, but at this point I don't care about that and am not going to address this anymore as everyone has there opinion right or wrong, who knows and we know how many that there is, but the one thing after looking at your setup again interests me, looking at the trim pin, when your at WOT and on on plane is your motor being stopped from going down or in from that pin, just wondering if your motor is being allowed to go down or in far enough, I know it should be able to with that wedge in there, but without seeing this in action I can only guess, hard to tell..

From what I can interpret here in this forum there are many variables on how any of this can be done for improving anything a person wants to do on his or her boat and what works for me may not work for you and visaversa and do try to take all advise here at face value as there are plenty of been there people on here and I respect their input as I will never be able to learn it all and in most cases don't want to, I just try to keep a perspective and am glad we have this information available to all of us to enjoy and pass the time with..

The main this is to enjoy your boating experience

i will trim it all the way down tonight, but i think its going all the way down till i run out of trim..i dont think the pin is stopping it,,but will double check just to make sure...

 

[WIMUSKY]

Re: is motor installed correctly? have porpoising problem at higher rpms

I am not going to claim I'm a pro at this, but c'mon guys, this is a 17' with a 50hp. In NO WAY should he need to add stabilizers like a doel-fin or tabs nor should he need to relocate batteries and weight forward. If this were the case then boats would be like this from the factories. IMO start with mounting motor with the correct length shaft (which he appears to have) CORRECTLY to the transom.

Removing the wedge will properly place the clamp on the transom forward of current position and justy a bit lower. This also looks like it will eliminate the potential steering arm rubbing issue by moving it slightly forward of the transom cap. Who says the PO mounted the motor correctly?

I agree. I don't think I've ever seen tabs on a 16/17' aluminum fishing boat(I know others will say otherwise, which is fine. It's just not the norm.). I have seen fins. However, if the motor on it now weighs a fair amount more than the original motor, that could be the issue. As someone said, excessive rear weight on a smaller boat can adversely affect the running attitude of the boat. Add a lighter hull, which this seems to be, and the problem is multiplied. Maybe the OP can research the weight difference in the motors to see if it's a potential issue or not. I would have no problem adding weight to the bow. On a lighter boat it will add stability while underway, especially in rougher water. I'm not keen on that wedge either. JMO

Definitely check that trim. If it doesn't tuck in all the way, that could very well be your problem...