Engine mount height

Roy & Dixie · Posted: Fri Mar 08, 2013 8:55 am Post subject:

I'll be very interested to hear how that works, as I think then it will be around where mine is (which I have not had a chance to try). When you get yours raised by 1", would you mind measuring the distance from the top of the transom cap to the center of the second-down engine mount hole? I'm just curious to compare it more precisely to mine.

Yesterday I got 2 big jobs accomplished, and they both turned out to be a lot easier than I had feared. I'll give an update on the engine raise here. This is how I accomplished it:

1) Lowered the tongue of the trailer as far as it would go.
2) Trimmed the F80 to be very close to parallel with the angle of the transom of the CD. The trim angle would allow the weight of the engine to lean onto the transom, not pull away from it after the 2 top bolts were removed. A 6x6 timber and a 2x6 filled in the space between the ground and foot of the F80.
3) The top 2 bolt's nuts were removed and the lower 2 bolts were loosened to the point that nuts were flush with the end of the bolts.
4) My wife slowly cranked the trailer tongue up, moving the stern down. As the weight of the engine was moved to the timbers, I was able to remove the top 2 bolts by backing them out with a wrench. The threads were sealed into sealant/calking.
5) The trailer tongue was slowly raised until the next set of engine holes were moved up to align with the transom holes. I could easily fine tune the engine position to align the holes.
6) Measurement of engine height indicated another inch raise would be close to perfect. It looked like there was still space for the lower bolts to slide within the lower engine mount slots, so we raised the tongue further until the next, and final pair of upper bolt holes alligned. There was not a bit of additional space in the lower bolt mounts, but it was a perfect fit.
7) All bolts were installed and tightened.

The only thing I had to do for the engine to slide up the transom was to cut 1/4" more off the edge of the black plastic strip covering the top of the transom. The engine mount widens slightly as it is moved up.

The top 2 holes are 2 1/4" down from the top of the black plastic strip. The 2 lower holes are 8" down from the top 2 bolts. The holes through the transom must have been laid out with a template for the F80, everything was just too perfect to have been randomly drilled.

Now it's off to the river for another sea trial.

Roy & Dixie · Posted: Sat Mar 09, 2013 8:44 am Post subject:

After yesterdays sea trail: at 3600 rpm, a speed increase of about 0.7 mph (13.4 mph, up from 12.7 mph) with engine raised 2". This is with bow riding noticeably lower with PermaTrim/engine trimmed to almost max down. I actually lost 1-3mph by trimming engine up, which raised the bow. Top of PermaTrim now rides just 1-2" below water surface at this speed.

Sunbeam · Posted: Sat Mar 09, 2013 10:26 am Post subject:

thataway · Posted: Sat Mar 09, 2013 11:48 am Post subject:

Roy,
Did you get a chance to run the boat faster than 3600 RPM? What was RPM at WOT? The 13.4 mph may not be the ideal speed to run the boat at. Depending on the weight, I would want to see a bit more speed at that RPM--and I wonder where you are on the "planing curve"..With the bow down that much you may not be running the boat most efficiently. At a higher speed you may find the Permatrim rides on the top of the water. Still riding 1 to 2" below the surface, and bow down,--plus loosing speed as you trim engine up, makes me think you are not at ideal cruise speed.

Roy & Dixie · Posted: Sat Mar 09, 2013 1:59 pm Post subject:

Roy,
Did you get a chance to run the boat faster than 3600 RPM? What was RPM at WOT? The 13.4 mph may not be the ideal speed to run the boat at. Depending on the weight, I would want to see a bit more speed at that RPM--and I wonder where you are on the "planing curve"..With the bow down that much you may not be running the boat most efficiently. At a higher speed you may find the Permatrim rides on the top of the water. Still riding 1 to 2" below the surface, and bow down,--plus loosing speed as you trim engine up, makes me think you are not at ideal cruise speed.

I need to run at different rpm's and record my results. Earlier I had seen close to 5500 rpm WOT, so the prop should be about right. I agree the best speed/efficiency will be at a higher rpm. I was surprised to see speed not increase with less engine trim, so I must not have been well enough up on plane.

thataway · Posted: Sat Mar 09, 2013 5:30 pm Post subject:

Roy,
It will be interesting to see what WOT and higher speeds are. That engine should be close to 6,000 RPM at WOT, and I would think that a light boat should be in the high 20's at sea level at WOT.

Sunbeam · Posted: Sat Mar 09, 2013 6:06 pm Post subject:

Roy & Dixie · Posted: Sun Mar 10, 2013 8:40 am Post subject:

Yesterday I posted: After yesterdays sea trail: at 3600 rpm, a speed increase of about 0.7 mph (13.4 mph, up from 12.7 mph) with engine raised 2". This is with bow riding noticeably lower with PermaTrim/engine trimmed to almost max down. I actually lost 1-3mph by trimming engine up, which raised the bow. Top of PermaTrim now rides just 1-2" below water surface at this speed.

I don't know why I ststed "MPH' when I have both GPS's set for nautical speed. Thus my 13.4 was actually nautical x1.15= 15.4mph. That sounds a little better. Next time out I plan to run and record speed at each 500rpm increase at best speed trim.