Im a little confused about Mercury I/O installations.......?

Question

I have an Alpha drive. I am going to use a template to cut the hole for it in my transom. I was told that i should cut the hole so the center line of the driveshaft is 14.5 to 15.5 inches from the bottom of the boat. I am also under the understanding that the cavitation plate should be even with the bottom of the boat. if this is correct, my cavitation plate distance from it, to the center line of the drive shaft is 13.5 inches.... If i cut the hole so the center of the drive shaft is 14.5 to 15.5 inches, this will put my cavitation plate 1" to 2" above the bottom of the boat. Would someone explain to me what is the correct distance to place the centerline of the driveshaft in relation to the bottom of the boat and why?

Answer 1

2" is way to high. You want it as even as you can get it with the bottom of the boat when it is in the level position. Slightly above is o/k, slightly lower will give you more spray but will still be fine especially if you trim up a bit. Try to keep your tolerance within a half an inch either way and you will not have any problems.

Answer 2

Are you allowing it to hang straight as if you measure trimmed in it will throw off your measurement>Measure 2s cut once>go to a marina and see what 1 looks like that way you will have it correct to low drag roster tail> To high cavitation>

Answer 3

log on to MERCRUISER .com. get dimensions and details.

Answer 4

you do not give enough info to correctly answer this question. first of all is this a new install or a repower(if repower your limited to amount of engine mount height) second the ANGLE of the transom MUST be accounted for mercruiser says 10-16 degrees but 13 is optimal. there are also several other transom requirments that must be considered. normally from 1inch below to 1inch above the bottom of transom is prefered, but the ANGLE changes this drastically. I found my OMC drill fixture and diemensions, but  I cant find my mercruiser one. I will keep looking if you cant get info let me know. I would suggest calling mercruiser tech line and ask for an instalation guide(you should have gotten one with the template). if this is a high hp or critical install(expensive or hp boat) I would deffinately spend the extra money and buy mcm's drill fixture. it gives all critical pilot holes including the tricky steering guide holes(on top). ps the plate people keep refering to as "cavitation" is actually called a anti-ventilation plate. the place called bottom is also a difficult term as depending on hull type(vee,flat,semivee,tunnel) is not always the center or bottom most. there are also different specs for hull types