Thread subject: Whaler Central - Boston Whaler Boat Information and Photos :: New Engine on older boat
Posted by sailinlove on 09/05/10 - 6:10 PM
#1
Just finished removing my '72 Merc 800 and plugged the original transom holes from the old engine. Now ready to bolt on the new Merc 90 OptiMax, however the uppermost of the bottom 5 holes on the transom mount is 10" below the transom lip, while the bottom of the transom well is only 8" below the lip. Any attempt to drill holes through the lower bracket holes will not end up where I can attach washers and nuts.
Options appear to be use two bolts on each side of the engine using the uppermost and lowest of the upper 5 holes, and disregard any of the lower 5 holes. However Merc recommends using 1 bolt for each side of the engine through both the upper series of holes and 1 bolt through the lower series of holes for either side. This caused a bit of concern when looking at the new engine resting on the transom. Raising the engine would allow using the lower bolt holes, but would lift the cavitation plate above the bottom of the transom.
Have '72 Nauset 16 hull with new Merc 90 OptiMax. Suggestions appreciated.
Edited by sailinlove on 09/05/10 - 11:44 PM
Posted by John Fyke on 09/05/10 - 6:16 PM
#2
Your cavitation plate should be above the keel. What size is the boat? You may have to use lags on the bottom holes if you have to raise it too much. Check the personal pages for the size boat you have and see if anyone else is using that motor on theirs.
Posted by sailinlove on 09/05/10 - 11:00 PM
#4
Obviously I should have said, "would move the cavitation plate well above the keel". if I were to raise the engine sufficiently to utilize the lower green or yellow holes as indicated in the BIA standard mounting bolt pattern. As noted the cavitation plate is above the keel when the engine bracket is resting on the top edge of the transom. Since there appears to be a difference of opinion over whether or not to utilize lag bolts in the lower series of mounting holes, i was attempting to determine what was the recommended bolt attachment procedure for installing a new engine on an older 16' whaler? One says no problem using lags, another says use thru bolts? Would be unable to thru bolt through the lower holes of the new engine transom bracket on my older Whaler unless the engine were raised at least 2".
Edited by sailinlove on 09/05/10 - 11:04 PM
Posted by Joe Kriz on 09/05/10 - 11:13 PM
#5
The engine mounted all the way down is too low.
The upper holes should be about 1 7/8 inches down from the transom or 2 inches max...
If you raise the engine one hole, then drilling the lower yellow holes would be marginal as you can see. Raising the engine one hole raises the engine 3/4 of an inch.
There are ways to cheat here but not much. You can angle the drill upward slightly in hopes to clear the inside of the splashwell.
You can also use washers on the lower holes that have been filed flat on the bottom side to clear the splashwell.
Raising the engine 2 holes raises the engine 1 1/2 inches and allows a person to drill the lower Green holes... This can work with the right prop but might not work for everyone.
If you are uncomfortable doing any of the above, then use lag bolts on the lower red holes in the drawing. This will give you the standard hole pattern and allow you to raise or lower the engine wherever it needs to be.
Posted by number9 on 09/06/10 - 8:12 AM
#6
"The upper holes should be about 1 7/8 inches down from the transom or 2 inches max..."
FYI, one of my Honda Rigging Guides says the upper holes should be more than 1.3" from the top of the transom.
Posted by Tom W Clark on 09/11/10 - 6:03 PM
#7
Bill -- 1-7/8" *is* more than 1.3".
Posted by Geo on 09/14/10 - 5:10 PM
#8
Don't worry about the engine sitting higher off of the transom. It will be fine one hole up and you can try two holes up if you would like to experiment a bit.
Posted by Finnegan on 09/14/10 - 6:17 PM
#9
See my post #7 in this discussion:
http://whalercentral.com/forum/viewth...d_id=10914
Any of the Mercs 75-125HP are easy to mount higher, since these engines have a shaft length that is actually longer than the othere brands.
Scroll down to the section on "Real Mercury motor shaft lengths" in this article:
http://www.marinepartsman.com/install...-boat.html
As I said in my article, the CONTROLLING mounting height in these shallower splashwells on the older Whalers is the BOTTOM set of bolt holes on the engine, using the highest holes. Figure out where the bottom bolts must come into the splashwell, and use that dimension. Then select the hole in the TOP set of holes on the engine bracket, and use those. They will be either 7-1/4" above the lower holes, or 6-1/2" above the lower holes.
Mounting the engine in this way, I would strongly recommend purchase of a Laser II/Lightspeed propeller, 19" pitch minimum or higher.