Help With Motor Height

[Skins88]

Fellas,

Just had a couple Vrods mounted on my boat by Bridgeview. I wasn't happy with the performance. Low speed and high fuel burn compared to the old yamahas that came off. Went from 225's to 250's. Would expect same or better performance. Do the motors look low? They do to me.

 

[ship happens]

Yup

 

[searun]

Not an expert, but general rule of thumb is the cav plate should line up with the bottom of your hull. This link might help:

Outboard Motor Height Guide: Diagrams & Height Adjustment Tips

Correct outboard motor height is crucial as it affects the stern lift, drag, porpoising, quality of water fed to the prop, and thus optimal performance

www.epropulsion.com

 

[Fixit]

what Grady do you have? I just put twin 250 vrods on my 270 islander. im getting 1.7-1.8mpg with inertia eco 17"P. 49mph WOT. I had the same experience going from Yamahas tov rods. .3mpg less but quicker top speed by 7mph. my cav plate is parallel with hull but I think they could come up one hole.

 

[Skins88]

I didn't check the motor height to hull when it was out of the water. Mistake on my part, but I assumed they would get that right.

I have a 282. Couldn't get better than 1.1 mpg. Top speed was 35knts. Everything I have read says I should get 1.5 mpg and 40knts at least.

Coincidentally my dock neighbor has the same boat with 225 verados. His are mounted on the bottom hole. Mine are on the third hole up. About 1.5 inches different.

 

[Fixit]

what RPM are you getting at WOT? what props and pitch? what performance numbers does your dock neighbor get? 100% clean bottom? even a few barnacles can drastically drop your mpg

its essential these motors get up to their rated rpm. I was getting 5700 rpm with 14.6"x19"p enertia props. swapped them with 16x17" enertia eco props. got 6000rpm and my WOT went up 5mph and mpg increased from 1.3 to 1.7mpg at 4000rpm. I wish they made 16"p eco props. I suspect you'll need 15"P props. some rev 4's would be ideal

 

[wdlfbio]

I had a 2007 282 with F250s. Loaded up for tuna with 5 adults and she was 1.1 - 1.3 mpg all day long, 25-28 mph. I think the best I got was 1.5 mpg super light and on a flat lake.

Those lowers look buried. I bet you could trim up near 60% without the props slipping…

 

[salmonkiller01]

Looking at the pics can most likely come up two holes in engine height

 

[Skins88]

what RPM are you getting at WOT? what props and pitch? what performance numbers does your dock neighbor get? 100% clean bottom? even a few barnacles can drastically drop your mpg

its essential these motors get up to their rated rpm. I was getting 5700 rpm with 14.6"x19"p enertia props. swapped them with 16x17" enertia eco props. got 6000rpm and my WOT went up 5mph and mpg increased from 1.3 to 1.7mpg at 4000rpm. I wish they made 16"p eco props. I suspect you'll need 15"P props. some rev 4's would be ideal

Wot 6100 rpm and 35 knts. Solara 3 blade 17p props. So rpm is fine but speed is low.

 

[Skins88]

I had a 2007 282 with F250s. Loaded up for tuna with 5 adults and she was 1.1 - 1.3 mpg all day long, 25-28 mph. I think the best I got was 1.5 mpg super light and on a flat lake.

Those lowers look buried. I bet you could trim up near 60% without the props slipping…

I tried adjusting the trim. I found raising them would make rpm go up and then at some point go back down. If I was trimmed up and then lowered it was like hitting the brakes.

 

[ship happens]

I would just send it all the way to the top. I bet that's where you'll end up anyway.

These type boats always need a combination of trim tabs, prop choices, and engine trim and there's always a sweet spot. Engine height just fits in there somewhere and all boats are different.

 

[Skins88]

I would just send it all the way to the top. I bet that's where you'll end up anyway.

These type boats always need a combination of trim tabs, prop choices, and engine trim and there's always a sweet spot. Engine height just fits in there somewhere and all boats are different.

That's what I'm thinking. Props may need to be swapped after.

 

[Skins88]

Appreciate the input guys. Will help me feel confident when discussing with Bridgeview next week.

 

[ship happens]

That's what I'm thinking. Props may need to be swapped after.

Yup 4 blades get that stern up

 

[wdlfbio]

I tried adjusting the trim. I found raising them would make rpm go up and then at some point go back down. If I was trimmed up and then lowered it was like hitting the brakes.

I don’t understand this. What I meant was that if you can trim up a ton (60%+) then your motors are way too low. You can raise the motors, which will reduce drag. That will likely cause an increase in WOT RPM. You don’t want a setup where you’re able to over rev. So, you can raise the motors, then adjust your prop diameter or pitch, which would likely Increase your efficiency or top end (depends on how you change the props). So, you will have more work to dial her in after raising the motors.

 

[Skins88]

I don’t understand this. What I meant was that if you can trim up a ton (60%+) then your motors are way too low. You can raise the motors, which will reduce drag. That will likely cause an increase in WOT RPM. You don’t want a setup where you’re able to over rev. So, you can raise the motors, then adjust your prop diameter or pitch, which would likely Increase your efficiency or top end (depends on how you change the props). So, you will have more work to dial her in after raising the motors.

I thought you meant I had them trimed all the way down. I think we are on the same page. Raise the motors. Then then wot rpm will likely be to high. Like ships mentioned, 4 blades might be the way to go.

 

[Bifmalibu]

Don't 4 blades generally increase rpm? Or have I got that backward? I went to 4 blade on my Arima and my rpm went up about 500.

 

[MikePA]

Don't 4 blades generally increase rpm? Or have I got that backward? I went to 4 blade on my Arima and my rpm went up about 500.

It would decrease if the diameter is in the same ball park

 

[Bifmalibu]

It would decrease if the diameter is in the same ball park

That makes sense, I think I went from a 3 blade 13 to a 4 blade 15 pitch.

 

[ship happens]

Surface area is pretty much the same as diameter. More surface area more resistance. Typically with 4 blades you go smaller diameter. It's literally just square inches of surface area.