Porposing & vibration problems. Walleyhead & Dhadley help!

[Mike83]

Hello,<br /><br />First time out with the boat this season today. Using the new (to me) 20" Raker that Walleyhead suggested last year. Same porposing problems as before. Anything less then WOT and it porpoises. Trim dosent matter much, it will still porpoise trimmed down. At WOT it's a different story. Rides like a charm, at any trim. (I can fly at WOT trimmed all the way up and the motor dosen't even bat an eye.)<br /><br />Boat is a 1994 Skeeter SS90 with an 110 HP V4 'Rude. Prop is a 13.5" x 20" Raker. Max speed is a hair under 50 mph at about 5600 RPM.<br /><br />Been thinking motor height. It's mounted on the second hole. (Can go up 2 more) AV plate is in line with the bottom of the hull. Can engine height help porposing?<br /><br />Second question: At about 3000RPM the whole boat vibrates. Prop is in good shape (a few minor nicks but nothing serious.) Is it possible for them to come out of balance?<br /><br />Thank you

 

[walleyehed]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

at 3K I'd guess you're just on plane or just breaking over....<br />Could be a slight bend in 1 blade, I'm not sure...My Rakers all run smooth as glass.<br />I don't have to trim all the way down, but mine does about the same thing at less than WOT if I don't trim down some.<br />Porpoising usually means something on one end is fighting the other end...mainly balance.<br />In my case, the higher I went with the engine, the better it got, but never "quit". I've wrote that off to a high performance prop doing it's job at WOT.<br />It sounds like you need to go up a hole and test.<br />Let's see what Dhadley thinks, but I think we're still too low with the engine..

 

[Dhadley]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

It's sort of odd that the boat doesnt level out with negative trim at slower speeds. All the indicators are there to suggest going higher. I'd try it and see what happens.<br /><br />There aren't any wedges between the motor and the boat are there?

 

[Mike83]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

No wedges. Would a Stingray/Hydrofoil/whaletail fix it? Do these devices reduce speed? Some say yes, some say at plaining speed they're not even in the water...

 

[Dhadley]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

The fins are a double edged sword. A fin is a tool that should allow for a higher X dimension. If the fin is small enough it won't hurt top end if it's too low but it may be too small to be effective. <br /><br />If the fin is below the waterline at speed it probably will slow you down (drag). <br /><br />I do like the larger fins like the King Fin but if you don't have a jackplate, don't bother. You'd be amazed at how high a motor will run with one of those.<br /><br />I'd test with more height. Raise the motor and see how your boat responds. The Smart Tabs may be worth looking at.

 

[Mike83]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

No place to mount smart tabs on a bassboat like mine. It dosen't have much of a transom to mount them to.<br /><br />I'll try with the motor height.<br /><br />Also the boat is very stern heavy. Not much i can do about it it's a very low profile boat with little storage area. (Next to none in the bow.) Would that hurt?

 

[Dhadley]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

Perhaps a 4 blade prop would help. They tend to have added stern lift.

 

[Mike83]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

So my raker wobbles if you spin it by hand. Can a prop repair facility fix that?

 

[walleyehed]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

Yes, if the hub is the actual problem...

 

[Jdeagro]

Re: Porposing & vibration problems. Walleyhead & Dhadley help!

Mike83;<br /><br />We also make Mobster Tabs with different plate designs for bass boats. send a pic of your boat to info@nauticusinc.com and I will try to help.