Boat Motor setup

[Riprap]

Thanks Nav, you know how the boating guys are - "I promise you, you won't believe the difference.......tralala...".
Time will tell sure enough!

[Riprap]

I cannot believe the difference a bit of weight can do to a boats performance! This past weekend, ¾ full fuel, 3 kids plus myself and without water in the well, the hole shot is brilliant and one would swear that the motor/prop combination was tailor made for this extra wide hull which the Seeker 480 has. As soon as the well is full, I have to put some kids right up front and when she gets to take-off speed (3 000 rpm) I trim her up a bit and the Dreamliner gets a bit of lift and her ass eases out the water!
As mentioned in the beginning, the optimax is 37kg heavier than the old 75/90 (same motor) but herewith another comparison:

115 Optimax:
84.5KW
170 kg – 0.5 KW/kg
Gear ratio 2.07 : 1

75/90 Merc ELPTO
67KW
137 kg – 0.49 KW/kg
Gear ratio 2.33 : 1

What’s important here is the gear ratio which is basically revolutions of the flywheel: revolutions of the prop. The gear ratio works in conjunction with the prop to convert power head energy into forward propulsion. Mercury have apparently lowered their ratios (higher numerically) so they could run more efficient higher pitch props. The lower ratio for instance with the ELPTO’s results in more torque at the prop.

Shannon had the same boat and his performed well with a 90 hp and as I stated earlier, my 75 with a 4 blade solas 13X17 was actually better than the nice bigger setup I currently have. I could just go down to a 17” pitch and be careful to not gun her and over rev the motor! I am concerned about the extra strain placed on the optimax at take-off. Should I be concerned about throwing bearings etc. when this motor labours so much to get wing lift when we are full??

I’ve just become aware of two ELPTO 90’s (less than 100 hrs.) which might become available and they are rigged with 4 blade Solas 13x17” props – same as I had. It will be a bit heavier on fuel but one has to fish a lot to validate the saving on the more expensive, newer technology motors!

What say you learned fellows?

[adensmith]

One of the most popular boating motors, outboards are great for smaller boats. Outboard motors offer lightness, power, and quietness all in one package. These motors are usually mounted to the boat transom, although there are some boats that provide the option to have an outboard motor well, or a motor mounting bracket.

[Q]

Where's my gun? Wanna to shoot dem spammer!

[Riprap]

One of the most popular boating motors, outboards are great for smaller boats. Outboard motors offer lightness, power, and quietness all in one package. These motors are usually mounted to the boat transom, although there are some boats that provide the option to have an outboard motor well, or a motor mounting bracket.

What you on about boet........!? :blue-rolleyes:

[Riprap]

I cannot believe the difference a bit of weight can do to a boats performance! This past weekend, ¾ full fuel, 3 kids plus myself and without water in the well, the hole shot is brilliant and one would swear that the motor/prop combination was tailor made for this extra wide hull which the Seeker 480 has. As soon as the well is full, I have to put some kids right up front and when she gets to take-off speed (3 000 rpm) I trim her up a bit and the Dreamliner gets a bit of lift and her ass eases out the water!
As mentioned in the beginning, the optimax is 37kg heavier than the old 75/90 (same motor) but herewith another comparison:

115 Optimax:
84.5KW
170 kg – 0.5 KW/kg
Gear ratio 2.07 : 1

75/90 Merc ELPTO
67KW
137 kg – 0.49 KW/kg
Gear ratio 2.33 : 1

What’s important here is the gear ratio which is basically revolutions of the flywheel: revolutions of the prop. The gear ratio works in conjunction with the prop to convert power head energy into forward propulsion. Mercury have apparently lowered their ratios (higher numerically) so they could run more efficient higher pitch props. The lower ratio for instance with the ELPTO’s results in more torque at the prop.

Shannon had the same boat and his performed well with a 90 hp and as I stated earlier, my 75 with a 4 blade solas 13X17 was actually better than the nice bigger setup I currently have. I could just go down to a 17” pitch and be careful to not gun her and over rev the motor! I am concerned about the extra strain placed on the optimax at take-off. Should I be concerned about throwing bearings etc. when this motor labours so much to get wing lift when we are full??

I’ve just become aware of two ELPTO 90’s (less than 100 hrs.) which might become available and they are rigged with 4 blade Solas 13x17” props – same as I had. It will be a bit heavier on fuel but one has to fish a lot to validate the saving on the more expensive, newer technology motors!

What say you learned fellows?

Apologies for bringing this back up but I never got any advice and the 90's are now available. It may seem like a downgrade but an improvement in hole shot is what is important for sanity sake and engine health, or what? Would value some advice?

[Navrik]

I am sure one of the experts on the site will comment soon.

[Riprap]

Deal done. It may seem like a downgrade but I'm prepared to burn a bit more fuel on an older smaller motor to match the boats requirements and the Amatola is looming and anyone can win that boat.......
I am now "forced" to sneak a Friday evening fishing session in so that I can measure cable lengths and the like. Apparently one has to be on the water, rod in hand, cold one at the console, dancing largie at the other end of a pole to do this! :eusa_dance:

[Navrik]

I am now "forced" to sneak a Friday evening fishing session in so that I can measure cable lengths and the like. Apparently one has to be on the water, rod in hand, cold one at the console, dancing largie at the other end of a pole to do this! :eusa_dance:

Sounds about right to me Rip :eusa_dance:

[Riprap]

Yep Nav, school's out, my crew are waiting!

[Riprap]

So I did what others thought was crazy and regrettable, The 115 optimax came off and on went a second hand merc 90 ELPTO (older 2 stroke technology).

First test was with a Merc Vengeance 3 blad 18" pitch prop - boat fully loaded and hole shot wasn't too bad but cornering was problematic with cavitation and at about 5 200 rpm the prop ran out of steam and there was no extra speed up to a max of about 5 700 rpm.
Second test with my Solas 4 blade 19" pitch - hole shot was perfect even with extra crew and max revs (wot) about 5 500 - 5 600 rpm and about 65 km/h - didn't check on the gps. Handling excellent and now I must just get used to that noisy two stroke again as the opti spoiled me.....

This just goes to show that sometimes a boat / motor configuration cannot be matched at the expense of other issues. I could have swung a lower pitch prop on the opti but with my kids going to use the boat in the near future, I was not about to take the chance whilst knowing full well that the motor would over rev @ wot. Speed is not everything! There should be some change from this deal which is another positive and with the lazy hull and motor now matched, we should hopefully have many years ahead of trouble free fishing.
The biggest mistake I made was listening to bad advice that a bigger motor would deliver better performance! I think I've proved the contrary......

[Navrik]

Glad you got something that works for you Rip!

Think you just cured me of trying a 200VMax on my Splash :eusa_doh: