hight of outboard??

[P2]

I,ve noticed on these boards the talk of hight of prop. Is there a formula or rule to follow for setting the hight of the motor / prop? Cavitation plate hight in relation to hull? Thanks

 

[Dhadley]

Re: hight of outboard??

There is no set formula. Each hull and prop configuration is different. Setback also plays a big part as well as intended use. Usually in recreational boats we refer to the location of the anti-ventalation plate (cavitation plate) in relation to the keel. With hi performance rigs the X dimension, or height, is refered to as the location of the propshaft in relation to the true bottom.<br /><br />In reference to recreational boats, years ago the rule of thumb was to start with the AV plate even and with a "good" prop you might get up an inch or so. With todays props it's not unusual to be able to run a motor on a given hull high enough that it has trouble picking up water yet the prop stays hooked up.<br /><br />The AV plate should not be below the keel. Thats when you start getting water up the transom and stand a good chance of having the motor injest water.

 

[P2]

Re: hight of outboard??

Thanks Dhadley. <br /> I should have noted I have a 20' cuddy wuth a 200 hp yammy on a sea bracket quite far back. Thanks again

 

[Dhadley]

Re: hight of outboard??

OK, heres where the set back plays a big part. As yu go back you can also go up. A very general rule of thumb is for every 5" you go back (offset) you can go up 1". "Quite far back" usually means about 30" - 32" or so. Lets say that it's 30" back (easier on my math skills). For a good starting position you'll be looking for the AV plate, when parallel to the keel, to be about 6" up.<br /><br />Then we're back to the hull / prop relation. The more V, the higher you can run the prop, generally speaking. The more technology in the prop, the higher it likes it. <br /><br />And intended use. If you're always in fairly smooth water you can be on the higher side. If you go in rough water, especially in following seas, you'll fudge to the short side.