Change in Engine height

[Navigator]

Currently my captivation plate is flush with the bottom of my hull (Welded Aluminum Modified V john boat w/ 40hp Honda). I know this is the recommended position. But here is my question:<br /><br />In most boats, when you run full throttle, the captivation is right at the surface. When I run full throttle, because I cant get that type of speed, the captivation plate runs about 2-3 inches "Below" the surface of the water coming off the rear of the boat. This is due to the weight in the boat in the rear. Since this is a tiller engine, the weight cant be moved forward. Anyways, would raising the engine another notch or so increase the speed due to less drag. Currently In sharp corners, I occasionally catch air so I'm not sure if raising the engine would help anything.<br /><br />Anybody have any experience with this scenario?<br /><br />Thanks,<br />Nav

 

[JB]

Re: Change in Engine height

Ahoy, Nav! Haven't seen you much lately.<br /><br />The plate you refer to is correctly named the "anti-ventilation" plate, for reasons that will become clear.<br /><br />The reason for starting engine rigging height (What DHadley calls the "X" dimension) with the AV plate even with the bottom is the expectation that the boat might be fast enough to put the plate exactly at the top of the water coming off the stern. If this is true, the plate prevents the prop from breaking the surface and ventilating.<br /><br />In most boats, including yours and any boat with a setback engine mount, the water is above the keel level before the AV plate and the prop come along. <br /><br />Those boats can gain speed and reduce drag by raising the engine to the point that the AV plate is even with the top of the water at WOT. This is especially advantageous with fixed trim engines.<br /><br />Try raising your engine a "hole" or two and try it out. If the prop ventilates ("Blows out") it is too high.<br /><br />Good luck.

 

[LubeDude]

Re: Change in Engine height

Ya just never know until you try it!

 

[Navigator]

Re: Change in Engine height

Ahoy JB, long time no talk.<br /><br />I haven't been around as much as I'd like to since the new baby. Now that He's one and the little tyke is walking, I'm getting more and more free time <br /><br />I was going to try raising the engine anyways since it is sitting in the driveway right now. Just thought I'd see if there were any negatives I didn't know about.<br /><br />Thanks guys,<br />Nav

 

[Navigator]

Re: Change in Engine height

Just wanted to give an update.<br /><br />I raised the Engine so the AV plate is about 2 inches higher then the bottom of the boat.<br /><br />I just clocked a 4mph GPS increase in top end speed with no negative side effects! <br /><br /> Now the plate is running right at the surface of the water!<br /><br />Nav

 

[walleyehed]

Re: Change in Engine height

Well done, Nav!!!<br />Have fun, and enjoy!!

 

[Dhadley]

Re: Change in Engine height

And the 4 mph increase costs how much?<br /><br />Good job!!