What causes a boat to porpoise

But can the prop cause it to porpoise. The only time I even use my tabs is to correct the list when more weight is on one side.

A boat can porpoise because the weight in the boat is disproportionate between the bow and the stern.

What causes a boat to porpoise. A boat can porpoise because the weight in the boat is disproportionate between the bow and the stern. It might also be because of the trim angle of the engine and the mounting height of the engine difference. What Causes Boat Porpoising.

Most of the time the boat is porpoising because its center of mass is too far out in the front. That makes the forward tip fall lower than it should causing it to porpoise. There are many aspects that can trigger this happening.

Porpoising is the result of the motors outdrive pushing the boat upwards essentially boosting it out of the water albeit for a short period of time. Once the boat comes back down the outdrive will once again push it back out of the water. What causes a boat to porpoise Basically two root causes for porpoisingmotor trimmed out too far or the hull has a hook in it.

Speed also plays into the equation. Even a boat with a hook in the hull will run smooth if you run her slow enough or dont have too much HP on the back. Secondary issues are running the motor too low.

Thanks 0 Quote Reply Posted. I always thought porpoising was caused by too many rpms causing the rear of the boat to lift out of the water above its plane angle which is determined by hull length and causing the bow to dip down in the water and then bounce back out. Tuck the motor all the way downget up on planeraise the motor trim bit by bit until you start to porpoisedrop the motor trim by the merest amounts until the porpoising stopsnow you can fine tune with your tabs while keeping your hull efficient maximizing speed and fuel burn.

May 18 2010 at 312 pm 872729. I had the same problem with a tin boat I had. What we did was put some wedges on the bottom where the transom meets the bottom and that will force the front end down.

If you run your band across the bottom of most glass bassboats there is what they call a hook manufactured in to the glass. Porpoising begins as you motor picks up speed and raises your boats hull from the water reducing the amount of hull in the water – which means theres too little hull in the water to support the boat. Trim the motor down until the boat stops bouncing.

Unpowered the most common cause of porpoising is a CG thats way too far forward and a lot of up elevator trim used to compensate. Add power to that mix and the problem gets even worse. Forgive me if this sounds purist but I suspect that the underlying source of the problem is having a motor on the front of an otherwise nice little sailplane.

Some boats do this. I had a mitzi 17 one of the many problems I had with it was chronic porpoising. I tried everything moving weight around dif trim angles moved the motor up hole by hole and back down hole by hole dif props wedges hydrofoils checked hull for hook.

Finally put trim tabs on to control it but of course you lose some speed. Excessive WEIGHT makes low-to-midrange porpoise BAD. Weigh the boat on the trailer then weight the empty trailer then subtract.

I still say its probably holding water somewhere. Hump Zone - All high performance boats experience a shift in dynamic center of gravity as they accelerate through what is called the hump zone. The onset for the startup of porpoising is usually triggered by a significant change in the dynamic center of gravity.

On most boats this trigger is the velocity that defines the hump zone. Take the boat back and have them re position the tab on the back of the boat. Do a water test to make sure its done.

Trim Tabs are nice but they shouldnt be the reason your boat doesnt porpoise. The only time I even use my tabs is to correct the list when more weight is on one side. My understanding is that porpoising is the result of a boats COG being too far aft andor the wetted surface not being large enough to support the weight of the boat on plane.

I believe Ive also read that if the ratio of transverse waterline length to longitudinal waterline length hope I stated that correctly is too large it can also contribute to porpoising. Boats porpoise for a few reasons. First the design of the hull can contribute to the frequency that your boat porpoises.

Boats with flatter bottoms are more likely to experience porpoising than boats that feature steep rises in their hulls. Porpoising may also occur when the trim on. It had a few nicks from an incident involving a shallow boat launch and not trimming the motor up.

So I had the shop machine the prop and polish and all. It looks brand new. But can the prop cause it to porpoise.

It looks about the same it just looks like the shaved down the nicks and welded it smooth. Any idea if this could affect it. Porpoising comes from a rapid change in the location of the center of Lift as the boat accelerates.

The location of static weights is one way of dampening the rate of change of the CofLso its not always obvious whether to move weight fore or aft in order to cause the dampening. A motor that is too big and heavy will way down the stern and cause porpoising while one that under-powers the boat will cause porpoising when trying to get on plane. Ensure the load is distributed properly on the boat or try moving gear and passengers forward.

Wheres your motor mounted. Most causes of porpoising are running to much pitch of prop weight distrubution and motor mounted to low. The two commonest causes of porpoise mortality that could be identified by our informants were boat collisions and by-catch in fishing gear.

These two factors are certainly responsible for high levels of porpoise deaths in the Yangtze. As long ago as 1892 a European observer reported that Yangtze fishermen used rolling hook long-lines to snag. You said no prop change.

If you had a prop generating some lift and changed to one that didnt that could cause the boat to now porpoise. The odd part is that the boat did not porpoise and now it does. You answered the questions I would ask but one.

Did anything change moved or took out weight in the boat etc. Moving the LCG aft. It can cause the boat to porpoise.

Any hook rocker or surface roughness on the bottom particularly in the all-important center-aft portion critical bottom area Figure 7-21 will have a negative effect on speed often costing several miles per hour on a fast boat. What causes porpoising. The prop needs to be setup for what ever boat its on or the right prop installed.

Whats happening is the prop grabs some water. As the water travels to the tipsthe bow comes up. Then the water flies off the tips and drops the bow.

Hence the porpoising effect.