Boat Hop .. Motor height ??????

been trying to solve my boat hop .. above 40 MPH. I have a Baja sun sport 18 ft with a 150 merc 1984 . Both motor and boat seem to be a pair matched from birth. If I trim the motor up to get the bow out of the water a bit the boat will hop madly. I installed a Hydro plate on the motor. abo****ly no diffrence. I have read the motor height may effect this bout I sure am nervious about cuttin 2 inches off my transon just to see if it will help. The hull is simular to a bass boat hull. Any thoughts ? I hate to put trim tabs on. I trailer the boat and go to many difftent lakes and beach the boat to swim and stuff like that. Help

Re: Boat Hop .. Motor height ??????

I really dont think you need to cut the transom to raise the motor.<br /><br />It sounds like your hull is begging for more lift from the prop. What kind are you running? Please dont tell us a Ballistic......<br /><br />What is your X dimension? (Cav plate in relation to the bottom of the hull when parallel)<br /><br />Good luck!

Re: Boat Hop .. Motor height ??????

Dhadley. U may not b aware of it, but your attitude, between the lines, makes my day

Re: Boat Hop .. Motor height ??????

prop is a SS 13.25 x 21 I dont see a name brand. I had thought of a diffrent prop for mor lift. Would the plastic props(Compuprop or Parana) give as much lift as a SS ? Like I said I run in a lot of diffrent lakes and rivers, having the plastic props gives a bit of safety to the lower unit. I guess I would spring for a new SS if I knew that it would fix the problem. BTW the engine RPM is 5300 RPM at about 53 MPH while I am holding on tight.

Re: Boat Hop .. Motor height ??????

Thanks UU! <br /><br />Maximerc -- what do the tips of the blades look like? Are they round or does it look like the tips are cut off? And look at your X dimension. <br /><br />Baja's and Checkmates go pretty good with moderate power but tend to get squirely at some point.<br /><br />I've never seen a plastic prop, or an aluminum one for that matter, have the lift of something like a Turbo. <br /><br />Let us know!

Re: Boat Hop .. Motor height ??????

I will have to measure the X when I get home to be exact but I know it looked to be 2 or 3 inches of hull below the Cavitation plate. <br /><br />I figured the plastics would not have the lift that a stainless one has. Tips are round. with just a touch of damage ,very little. <br /><br />The boat is rated at 175 HP.

Re: Boat Hop .. Motor height ??????

To Dhadley;<br /><br />Your "hop" is common with many power boats, and commonly refered to as porpoising. You can play with props, move the motor up and down, play with hydrofoils, or add engine extentions to the transom, but the answer lies in balancing the boat. Using the engine and / or the propeller to correct balance or hull design issues is an inefficient use of power. If the motor has electric tilt trim most owners will minimize the porpoising by triming the motor down ( under ) to increase the lift on the stern. This may work, but your are constantly running the prop at an angle which lessens the thrust, reducing top speed and fuel efficiency. Hydrofoils will lift the stern, the faster the boat moves the more lift and eventually causes so much bow pressure that the boat runs bow down, and bow steers (sensitive to port / starboard steering). You may not want to install trim tabs but they are the answer, because they change the hull configuration to compensate for load, speed, and water conditions. Exactly like flaps on an airplane, and you have never seen an airplane without flaps and trim tabs. It is all about balance. <br /><br />Your boat axis (balance point) is about three feet from the transom, so on a 18.5' boat you have a 15' leverage arm up to the bow that makes it easy for the water to push it up. Remember what comes up must come down, therefor porpoising. Lift on the stern keeps the bow from coming up. Remember the faster you go the more water pressure on the trim tabs or hydrofoil, so you will need to adjust the tabs accordingly (you will not be able to adjust the hydrofoil). The reason you did not get the correction from the hydrofoil is that your boat needed more than it can give (it is not big enough). If you use a bigger hydrofoil you will run the risk of cracking the cavitation plate which it is bolted to. <br /><br />Besides the cost issue of helm controlled trim tabs, they are generaly not offered on smaller fast boats because of the potential for misuse. If you are running at 35 to 45 mph and accidentaly deploy one tab, the results are serious. <br /><br />Check out Smart Tabs at www.nauticusinc.com (automatic self adjusting trim tabs for boats 22' and under) or do a search on this site to see what others say. They typically run $179 to $199 and are easy to install.

Re: Boat Hop .. Motor height ??????

Whoops John, your product may have some potential (unless when you need tabs to compensate for sensitivity to side wind - which your design seems to make worse).<br /><br />You should turn advertising to iboats' Marine Mega Mall or Boating Classifieds.<br /><br />Mods are not happy about ads in the Forum.

Re: Boat Hop .. Motor height ??????

If the engine is not hittin the water right the trim tabs are gonna make a ton of drag. Like tires on the front of a car yea you can force it to go straight.

Re: Boat Hop .. Motor height ??????

Before you spend any more money on gizmos & gadgets, check to make sure the bottom of the boat is true. The keel should be dead-on straight from the keel to the point where the bow begins to rise up. If you've got a hook or rocker in there it can be the cause of the hop in your ride. It doesn't take much, either! If the boat has spent it's life mostly on an improperly fitted trailer, 20 years can result in various imperfections in the bottom that affect performance...<br />Make sure that's not the problem before trying to put a band-aid solution on it when the problem lies somewhere else...<br />- Scott

Re: Boat Hop .. Motor height ??????

I have not checked the hull real close but it has a good trailer , bunk slide on. not saying this might not be the problem though will check.

Re: Boat Hop .. Motor height ??????

UU,<br /><br />Sorry if you feel it is Advertising, and I will avoid recommending products in the future. I would like to know how you got your experience with our tabs. I do know that a sister company on the west coast has used them and buys them through customer service. Tracking in any seas has been a strong point.

Re: Boat Hop .. Motor height ??????

Natiujohn, can you send me your e-mail address? I have a couple questions that are better asked off line from the forum...thanks...<br /><br />Kevin<br />kehite@gci.net

Re: Boat Hop .. Motor height ??????

Ok X height is 1.5 inches thats about the average with the V of the hull. Hull is arrow straight !

Re: Boat Hop .. Motor height ??????

Well, the hull wont be arrow straight (it will have some hook in it right at the back) but thats good. <br /><br />Try raising your motor. Raise it as much as you like to see what it does. Keep records of everything from feel to rpm to speed to trim range.<br /><br />It would be real helpful to know more about the prop.<br /><br />Keep us informed!

Re: Boat Hop .. Motor height ??????

Raising it ....... really???????

Re: Boat Hop .. Motor height ??????

For some reason I did not say that the engine cavitation plate is 1.5 inches ABOVE the hull.

Re: Boat Hop .. Motor height ??????

nautijon,<br /><br />Your preaching to the choir when it boils down to telling Dhadley about boat performance.<br /><br />He knows more about it than any memeber on this board.<br /><br />I believe your tab suggestion has merit. Some boats are just prone to porpoising. I know, I've owned two of them.

Re: Boat Hop .. Motor height ??????

Well, I think recommending or telling experiences on products is very OK indeed.<br /><br />Ofcourse one must adjust the recommendation for bias when it comes from a party with commercial interest in the product.<br /><br />Only mentioned the issue to warn you that board Mods normally take action on it.<br /><br />Over time I've seen or tested a number of trim tabs. Different shapes & sizes, different fitting, different systems - manual, semi-automatic, hydraulic, electric.<br /><br />IMHO you need a set in proper size that you can control individually. Either with a trim gauge or with handles that shows the applied trim alone by it's position. If you want to use trims for controlling uneven load, side wind, hull riding angle etc. you need to be able to control the trim tabs.<br /><br />I also find it very individual if trims are needed at all. Two different owners of the same boat make and model may not find it equally neccessary.

Re: Boat Hop .. Motor height ??????

gentelmen;<br /><br />My reponse should have been addressed to Maximerc who was asking the question, my error. I was not trying to offend anyone, just offering some experience. <br /><br />There is a major difference between fixed trim tabs, helm adjustable trim tabs, coil spring tabs, and water filled tabs, and nitrogen gass actuators in the performance characteristics. The nitrogen gas system is not recommended by the manufacturer for use on boats above 22' in length, because port to starboard control for longer & wider boats often requires major corrections. Example, one tab fully deployed and the other completely up. Trailerable boats have a narrow beam which is easier to control port to starboard. <br /><br />Assuming the boat was rigged correctly, there is no damage to the hull, a porpoising issue is likely a weight balance issue, especially if the porpoising stops when a load is added to the bow. <br /><br />I do not recommend adding any devise to a boat until the problem is correctly identified. Anyway I hope Maximerc finds the best solution, regardless of outcome.