Porpoising. What should I do?
- Thread starter Eco Geeko
- Start date
Pineapple Express
Well-Known Member
Based on what? The general guideline is that the anti-ventilation plate is 1/2 - 1" above the bottom of the hull. The stick isn't even at the bottom of the hull in his pic.
Pineapple Express
Well-Known Member
This is along the lines of what you're aiming for:
So the 2nd and 3rd pictures in my first post both show the motor trimmed fully down. The first video link starts with it fully down in the water, but it gets trimmed up as the video progresses.
The hull is little damaged in the back, you can see it pretty well in the picture. Its just the one dent.
My primary concern right now is the porpoising, not the hole shot. The only reason I bring it up is I think they may be related.
I'm not able to raise/remount the motor myself, so while I'm interested in doing so, its a more expensive option than some of the other solutions, especially if it doesn't work. So although Pineapple Express's 2 pictures just above present a good case that it is too low, I think I'll start with some extra weight in the bow, and this fin, since its easy to install and test. Then go from there.
Lots to respond to here from you guys. Really appreciate the feedback!
The hull is little damaged in the back, you can see it pretty well in the picture. Its just the one dent.
My primary concern right now is the porpoising, not the hole shot. The only reason I bring it up is I think they may be related.
I'm not able to raise/remount the motor myself, so while I'm interested in doing so, its a more expensive option than some of the other solutions, especially if it doesn't work. So although Pineapple Express's 2 pictures just above present a good case that it is too low, I think I'll start with some extra weight in the bow, and this fin, since its easy to install and test. Then go from there.
Lots to respond to here from you guys. Really appreciate the feedback!
myles
Well-Known Member
Like many others have said, move the engine up, it's too low. Add weight to the bow (move fuel tank, cannonballs, chain anchor or cooler w/cold beer???) and the boat will run perfectly. keep engine trimmed down fully then once your planing trim out a bit depending on conditions.
I'm sure you have a buddy with a chain hoist...if not summit tools sells them for under 100bucks. id say about a 12 beer project
reeltordarius
Well-Known Member
My vote, Bennett trim tabs
kaelc
Well-Known Member
I had a set of Bennett's ready to install on my boat and went the Dolphin fin, but the SE Hydrofoil route on my 18 foot Hewescraft. Eliminated proposing and really helped with getting on step. Sold the Bennetts, but my new boat has em!My vote, Bennett trim tabs
We have a new Dolphin Fin in Victoria for sale if you go that route, it doesn't quite fit the leg on our 150 Honda.
Pineapple Express
Well-Known Member
Can you access the inside to hammer out the dent? A hook in a hull is really bad news for boat handling. I suspect your porpoising is directly related to this. A fin on the engine may help, but the hull should be addressed.
kaelc
Well-Known Member
That is what I had on my 18 footer. Highly recommend it as a first step.
Aquaholic
Crew Member
Absolutely. Everything else is a bandaid. This is a mass produced boat and they must’ve made hundreds if not 1000 of these. This one particular boat is porpoising. A fin or tabs will be an added bonus.
Interesting... I don't know if I can get to it. I didn't think it was a big deal, but I will see what I can do.
From the pics you've provided I can't see hull damage that would give you your problem and your engines height is almost correct (within 1/2 inch) so that isn't the problem. Its just likely the weight of the engine and the easiest thing to try and it may well solve the issue is the dolphin on the leg.
Thunder21
Well-Known Member
I haven’t read all the posts so excuse me if everyone has said the same thing but Ive had the same issue as you in the past. I have a 17’ welded aluminum that we put a 115 Yamaha on that porpoised badly. Engine was too low so we raised it and we added a fin and it’s like a new boat .
Brando
Well-Known Member
If you can’t lift the motor anymore a 4blade prop will help lift the stern I would go that route before a fin but that’s just personal preference I did not like the fin when I tried it.
There are also manual jack plates available If your out of bolt holes..
you can lift the motor using the trailers tongue jack and a couple friends to support the motor. Place a block of wood under the skeg remove the bolts while your helpers support the motor raise tongue jack replace bolts and done. Just be careful and go slow.
There are also manual jack plates available If your out of bolt holes..
you can lift the motor using the trailers tongue jack and a couple friends to support the motor. Place a block of wood under the skeg remove the bolts while your helpers support the motor raise tongue jack replace bolts and done. Just be careful and go slow.
mbowers
Well-Known Member
I was interested in a pic with the straight edge on it to show height in fully trimmed down position but didn't make that clear. Trimming up changes the angle of the motor not just the height.
I thought I saw damage on both sides on the keel. If you can't bang it out maybe you can fill it in on the outside. I don't know what the right material would be though. Even if just temporary, if you could get the original hull shape back at least you would know if the dents are the problem..
Trim tabs on my hull were mounted just a little low by the idiot new owner of the boat company. That made the boat porpoise with tabs fully up when it didn't porpoise without the tabs. New owner tried to blame weight distribution. Talked to the original hull designer/builder and he confirmed that the dragging tabs caused the porpoise. The transom is just a super sensitive spot for hull design..
Aquaholic
Crew Member
the curiosity in me wishes you would've raised the motor first, tried it to see the results and then added the fin if necessary.
gungadin
Well-Known Member
In my experience porpoising is fixable in almost every instance.
Hull dents, motor height, propeller choice, weight distribution and degree of tuck under will all effect porpoising.
Hull Dents—fill or hammer out, yours does not look like it would affect the porpoising much if at all. The dent needs to affect the smooth flow of water and really needs to be in the form of a valley. This causes the waterflow to go downward rather then exit the hull cleanly.
Motor height- Your motor looks about a cm or so above the bottom of the hull, raising the motor one hole would bring it about 2cm +/-. Still within manufactures specs.
Propeller choice-- I don’t know enough about this to offer an informed opinion.
Weight Distribution- move weight forward, fuel tanks, anchor etc.
Degree of tuck under-- Your motor only tucks under 2 degrees, On some boats this is enough, on others it is not. You need to be able to tuck the motor somewhere between 12 and 14 degrees from vertical to be able to trim the motor in to eliminate porpoising. The transom will provide some of that tuck in. Transom angle varies with boat design. Older Boston Whalers have a shallow tuck angle on the transom about 7 degrees (if memory serves), you would need to measure yours to find out. Dolfin and the like force more water and thus increase pressure under the cavitation plate area forcing the bow downward. This may or may not cure your problem.
Using a motor wedge such as https://www.amazon.com/T-H-Degre-Positive-Transom-Wedge/dp/B0000C6I2T will add 5 degrees of inward tuck and allow your motor to tuck under the transom more, pushing the bow down and keeping it there.
Hydraulic or electric trim tabs basically have the same effect as a dolfin, but with the added benefit of being able compensate for more weight on one side.
Hull dents, motor height, propeller choice, weight distribution and degree of tuck under will all effect porpoising.
Hull Dents—fill or hammer out, yours does not look like it would affect the porpoising much if at all. The dent needs to affect the smooth flow of water and really needs to be in the form of a valley. This causes the waterflow to go downward rather then exit the hull cleanly.
Motor height- Your motor looks about a cm or so above the bottom of the hull, raising the motor one hole would bring it about 2cm +/-. Still within manufactures specs.
Propeller choice-- I don’t know enough about this to offer an informed opinion.
Weight Distribution- move weight forward, fuel tanks, anchor etc.
Degree of tuck under-- Your motor only tucks under 2 degrees, On some boats this is enough, on others it is not. You need to be able to tuck the motor somewhere between 12 and 14 degrees from vertical to be able to trim the motor in to eliminate porpoising. The transom will provide some of that tuck in. Transom angle varies with boat design. Older Boston Whalers have a shallow tuck angle on the transom about 7 degrees (if memory serves), you would need to measure yours to find out. Dolfin and the like force more water and thus increase pressure under the cavitation plate area forcing the bow downward. This may or may not cure your problem.
Using a motor wedge such as https://www.amazon.com/T-H-Degre-Positive-Transom-Wedge/dp/B0000C6I2T will add 5 degrees of inward tuck and allow your motor to tuck under the transom more, pushing the bow down and keeping it there.
Hydraulic or electric trim tabs basically have the same effect as a dolfin, but with the added benefit of being able compensate for more weight on one side.
Four-Reel Drive
Active Member
smart tabs could help:
Buckethead905
Well-Known Member
I can absolutely guarantee you that the motor is too low... if it’s too low with the trim half way up why are we still having the discussion? The video clearly shows the cavitation plate buried under the water. Also take into consideration that keel shape and deadrise at the stern can play a part in the trajectory of the water when it exits to the aft of the stern. Look at the first pic, there shouldn’t be any water rushing over the top of the cavitation plate, do we need a group buy on glasses for everyone? I’ll take a photo of my boat running this afternoon if we get out.
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