I know my hull isn't designed to go that fast, and that's why it porpoises. At least with only one person and little weight in the front it does.How can I fix this.I'm debating between hydrofoil and smart tabs.I don't want to scrub any top end speed, and dont fancy breaking/drilling through my cavitation plate.Any thoughts?
Can you adjust the motor trim angle downward, closer to the boat?If not, you might want to cut a wooden wedge, and place it between your motor and the transom. A piece of wood is cheap and may give you the results you want.
What is your motor HP? Trimming the motor all the way down may reduce the porpoising but will also reduce the speed. Smart Tabs will give you better performance on the low end and top end, plus get rid of the porpoising.
Well, it's a '75 15hp. More like a 13hp.rated at prop.Because of the smaller displacement, it doesn't perform as well with weight in it, than say a 20 hp.(bigger disp.)I don't know the exact speed, but it's too fast to control when it porpoises. Plus, the main problem being, I am afraid when porpoising the air will get packed under the boat and flip her over, kinda like a sail!I know about smart tabs. I think they run about 130$CAN. Perhaps it's worth a shot.My boat's only 4 feet wide, so I kinda want to upgrade to a wider 12 footer, possibly with a V shaped hull(near the stern)I'll see what happens...Anyone had experience with smart tabs on a cartop?
hello I have the same problem with my voyager 14 6ft beam jon boat with a 35 rude and stainless 13 pitch prop. I found the only way to cut the porposing was to raise the motor on the transom and add weight to the bow. the other lesson I learned is 90 degree turns in the ditch ( about 10 ft wide) are impossible but long walks out of the marsh grass are good luck and have fun
I have a tiller handle made, but am a little leary the strength of the plastic twist grip piece. Plus, there is some free play in the twist throttle piece, and with that much leverage/extension there would be too much free play for my liking. Then, in tight turns, you have to swing that pvc pipe way out to one side in order to get a sharp turn. I'll think about it.-230$ (Can.)for trim tabs? I guess it's worth it.Thanks all for your suggestions!
Cartoper;$230.00 even in Canada sounds a bit high. The size you need is $99.00 in the USA from most major retailers. It is an easy Do it yourself install so that would also save money. Who are you going to buy them from? maybe i can help find aetailer for you. the cost should be well below $200.00 for the ST780-20
I had the same problem with my 1967 14 foot 67 inch wide boat with a 1975 15 HP Johnson.It was fine with some one in the front seat or middle seat but when alone the front was too light and out of control. Moving the gas tank and my tackle box up front helped.I made a big improvement for about $5. What I did was to just make my own trim tab out of a 1 inch square aluminum tube. I formed the tube a little so not quite square and to give it a little more down angle. I did not want to drill any holes in the boat so I glued it on with Silcone seal. I worried for weeks it would come off while running hard but it is still on there today. I used two 1 inch square aluminum tubes 1/16 inch thick from the chines to about 6 inches form the motor. In later years I filled each with closed cell fome so it would flote if it ever came off.With a buddy in the boat with me I could not tell the difference but when alone made a big difference. The bow while still light would no longer come way up and scare me. I do not know if the top speed is slower or not but can tell you for me I got to my fishing hole a lot faster. Before I was staying just up on plane and still kind of out of control. With the change I could go way over planeing speed and on nice day run full throttle.To give it a try and to make it eaiser to adjust your angle just get some 1 or 1 1/2 inch aluminum angle 1/16 inch thick. Only reason I used the square tube was so I could fill it with flotation and I though less likely to cut fishing line.
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My brother had a 13 ft raycraft with a 70 hp johnson. It porpoised at slow speeds and he had to drive it wide open to stop the porpoising. Too large of a motor on too short of a boat I guess.Also had a friend who had a 9 ft. fiberglass hydroplane with a 40 horse chrysler, porpoised real bad unless you put some weight in the front. Was water skeeing behind it and was on a slalom, it kept slowing down and my ski was sinking, I kept motioning for him to speed up and he said this #@$%ch is sinking. He couldnt slow down or it wouldn't make it to the boat ramp. I had to pull myself in with the ski rope and sit on the front of the boat to keep it planed. Got to the ramp and sunk it on the trailer. It had been patched and the patch peeled off.
Guys;You all are on track the problem with stern drive and stern mounted engines is balance. Get the boat in balance and most of the handling problems will go away. Unfortunately what balances the boat today may not work tomorrow when you bring your 100 lb dog. That is why fixed devices are a cumbersome answer. You will always need to make some adjustment or put up with a handling problem.The common attitude is that as long as the boat can get on plane it does not need trim tabs. That is a very narrow look at the benefits of trim tabs. Put enough HP on the but of an elephant and it will plane, but that does not mean it is going to handle very well. Permanently fixed planing devises(sand bags, metal strips and the transome, hydrofoils) will all provide some level of correction for a specific characteristic at a specific speed or under specific conditions, but they can degrade the performance under other situations. Since we operate boats in ever changing conditions (speed , weight, water currents, etc.) the control device should also be variable. This opens the window of effective use dramatically. That is why all airplanes have flaps and trim tabs. These variable surfaces changes the hull design to compensate for all of the changing conditions, as the plane moves through the air (which is a liquid too). Size of the airplane or boat makes little or no difference.
I agree Nautijohn, I think it comes down to what you want to spend, and what your looking to get. A $3 sandbag will stop the porposing (kind of) but it adds weight and its a static fix, a $50 hydroplane cuts the weight but it's still static, and a $150 set of tabs will smooth it out in most situations because its active. Take your pick, find the $$ amount that best describes how bad you want it fixed.
Envy83,Smart Tabs list prices range from 99.00 to 149.00 to 199.00. For this appication they would be 99.00 at most retail outlets. One last note adding weight to the boat or making it run bow down will increase fuel consumption, and it isn't free. Although the enginenis small and does not use too much to begin with, every time it is used it will cost more.
Just install a Stingray hydrofoil on the foot of the motor for about $35.00. Your boat will handle like a dream! I had an 18 hp Mercury on a 13 1/2' princecraft cartopper with similar problems. The hydrodoil eliminated the problem and made the boat extremely stable...especially in turns.
On a 16ft inflatible we have, a stingray hyrofoil has been added, and yes it does help keep the bow down etc.I would rather use the tabs though, seems a little better in the long run.Thanks for all the imput, now, time to make the decision...ps. I don't think my transom can handle any more pressure that a hydrofoil would apply! LOL
A boat as light as yours is going to porpoise when speeding. That's a fact of life.Lots of good ideas above, but I doubt you're ever going to fully solve the problem.
On my old flatbottom I put an 5 gallon container of water ( one of those plastic gas containers you can get for 10 dollars)in the front of the boat. You can add or remove water to get the right balance - worked great for me at a minimal cost.
Porpoising 12ft aluminum?
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