Transom Bracket - twin outboards

[Old'sCool]

My most recent addition is a Solas 19p 4 blade. I should have gotten the 17P though for all around. I have a 3 blade 17 and 19. The 17 allows more rpm at lower speed (rough water, slower ocean speeds) 19P offers a little lower rpm but faster (cruising/waterway speed)

[doodlebug]

I have tried lots of props I like the mirage plus sets
best but my starbord motor has a 135 ecu right now so it won't turn my 21 mirage plus so thats why the 4 blade
power techs after I get another 150 ecu if it still won't
swing the 21's i'll get a set of 19 mirages power techs
are 19's

[doodlebug]

Denny do you keep yours on the trim pad? I see the
tiedown.

[lobo1]

neutral trim, the motors are in the second hole from the top - I used a straight edge and a level from the bottom of the hull, right under the drain plug....I measured to the cav plate just like in Bushwackers picture. 8.5 inches is what I get......my straight edge runs just about down the centerline of the lower unit - right thru the center of the prop.

Each hole only gets me one inch. I have one up and two down to work with- any ideas - now that you know what I have?

Sounds like I have a mess

[doodlebug]

best option is to run it and see where cav plates are in the water ajust until they are above water then try some different props if geting water level set right doesent
fix it

[Bushwacker]

I'm running a 15x15 4B PowerTech. Blades supposedly have the old OMC SST profile. I ran an SST on my old 115 and it was an excellent prop. Not sure it's the optimum prop because it's about 0.5 mpg worse than my 14x20 Michigan Apollo 4B, but it seems to have decent stern lift, turns about 5450 with max load, gives me an awesome hole shot, gets on plane at only about 40% throttle, and lets me plane at about 12 mph with a very heavy load, which is nice in rough water. The Apollo seems to have even more stern lift even though it's supposedly a bow-lifting prop. Would like to try a 4B Apollo with less pitch or a BRP Cyclone 4B to see if I could still turn max rpm at max load but get a little better mpg.

[Bushwacker]

Denny do you keep yours on the trim pad? I see the
tiedown.

Good catch Duane! But that's just a helical screw anchor hurricane tie-down, not the buried telephone pole that an M-37 trailer requires! Denny

[McGillicuddy]

Lobo1,
At the risk of being redundant here is a clarification with your picture altered.
My apologies if I got the wrong impression, but if you measured the height of your cavitation plates relative to the height of the bottom of your keel, you need to revisit that - I believe the base of measurement (where the straight edge lies)needs to be where the hull and transom meet directly fore of each motor.

Bushwacker's measurement is taken at the keel because that is where the engine is inline with the bottom of the hull (because he's running a single)

For twins set up the strait edge needs to rest on the bottom of the hull approximately where the white squares are in the picture.

[lobo1]

OK. I will re-measure. My number was so far off from the 3-1/2" you guys were talking about.....I feel kind of stupid - having measured to the wrong spot but at the same time feel a bit relieved. At least I can get somewhere in the ballpark measuring where you are suggesting. Will go back tonight after work for a do-over.

Thanks again

[JohnB]

Setting these up is trial and error, but I think your going to wind up at 3.5" plus or minus an inch. It also greatly impacts the performance of the boat, and the fuel economy so it is worth the time to get it right. Another symptom of the motor being mounted too low, or the trim being negative is the wheel is a little harder to turn. Maybe it is just my boat, but that is what I found.