Lund Rebel 1650 and Yamaha F90 - setup question

[e1e0n]

Can I raise motor on this boat? It has a lip on the top of the transom and motor will not be flush with the transom. Can I do something myself without a dealer? Dealer who sold me that boat is 2+ hours drive and I prefer to do this myself. Problem I am trying to solve is ventilation when trimming to max speed (vent plate not level at max speed + I am getting ventilation with slight turns). The vent plate is level with bottom now, I tried other prop but it did not help much. Boat handles good at lower trim but speed is lower by 3-4 mph. The max I am getting with max trim (and ventilation issue) is about 42 mph. To get good stability without ventilation I should go 38-39mph.

PS I had tried Michigan Apollo SS prop with same pitch I have (21) but it's a bit bigger in diameter (+3/8") and I think it felt a bit much for my engine. Also I calculated slip for prop ~0.05 seems a bit low?, is Apollo XPS actually not 21 pitch but somewhat more? It game me a bit better handling but RPMs are on low range (~5100 of 5000-6000). It seemed like if I raise the motor I should get better RPMs (at least in theory).

Thanks!

 

[SkiDad]

You can raise the engine without concern. But Ventilation will get worse if you go higher. I would try a turbo1 prop in 19 pitch. Or something aggressive like that prop. Powertech makes a few like the nrs and raf. A lot of the aggressive props are progressive pitch and act like next size up. Or if you want to go on the cheap side look at 21 pitch spitfire / nemesis prop.

 

[e1e0n]

Ventilation only happens when I trim to high to get higher speed. The anti vent plate is not level with water. I was thinking when I raise motor I will not need to trim that high everything will be level.

 

[e1e0n]

No Title

New 19 SS prop ... not vent issues. Top speed ~43 mph. Looking at my vent plate seems engine sits too low :help:

 

[steelespike]

Trimming up changes the angle of the motor helping it to get the boat up on the water better.trim up only just enough to get best speed.
What is the slip with new prop?Is the speed by gps?Any wind or currant aiding speed?
What is the rpm at 43 mph.Slip? Raising the motor can help speed a little ,usually because it was too low in the first place.
It may make trimming up more touchy about venting.
Raise it a hole and see what you get.

 

[e1e0n]

Slip 4.8% ??? Prop pitch probably 20? (It's Michigan Apollo SS)
RPMS 5800 (WOT range for F90 5000-6000)
Speed 43 Mph (by GPS)
Gear ratio: 2.31
Wind was moderate (speed was not affected by direction). No current (lake).

PS Noticed that I actually can't trim behind some point, the trim does not work (due very heavy force from the engine?) and there is no ventilation I even could not reach that point.

That was never a problem with my old AL prop.. I could trim up until it ventilates.

From the photo: does it look like engine is too low? I mean I almost can't see vent plate ... I've seen pictures where it's actually fully visible with slight splash from the water.

Trimming up changes the angle of the motor helping it to get the boat up on the water better.trim up only just enough to get best speed.
What is the slip with new prop?Is the speed by gps?Any wind or currant aiding speed?
What is the rpm at 43 mph.Slip? Raising the motor can help speed a little ,usually because it was too low in the first place.
It may make trimming up more touchy about venting.
Raise it a hole and see what you get.

 

[WIMUSKY]

Take a pic from the side with it on the trailer so we can see the AV plate in relation to the bottom of the hull. It does look a little low while underway. I believe mine is fully visible.....

 

[steelespike]

Hard to see but it appears the water is just below the "diverter plate" How big is the space between the diverter and the anti vent plate?
The final height would depend on the prop,hull design,typical load,balance and
water conditions.Height may vary between two identical models.
I would put the al prop back on and see if the full trim returns.
I would suspect the trim assembly before thinking the prop caused the trim malfunction.
If the prop caused the malfunction I would suspect the trim.

 

[e1e0n]

Take a pic from the side with it on the trailer so we can see the AV plate in relation to the bottom of the hull. It does look a little low while underway. I believe mine is fully visible.....

I don't have picture, but AV plate is absolutely level with bottom (lowest point of the hull).

 

[e1e0n]

I feel that I achieve max trim and exceed (I start to hear laud engine exhaust when I trim to "max" point). Trim works fine out of the water. I think the trim mechanism has limitation on force and in my case it just reached it level. AL prop is different, because with it I could reach less max speed = less stress on trim.

Hard to see but it appears the water is just below the "diverter plate" How big is the space between the diverter and the anti vent plate?
The final height would depend on the prop,hull design,typical load,balance and
water conditions.Height may vary between two identical models.
I would put the al prop back on and see if the full trim returns.
I would suspect the trim assembly before thinking the prop caused the trim malfunction.
If the prop caused the malfunction I would suspect the trim.

 

[steelespike]

I'm sure no Trim and tilt expert but in my opinion a trim unit for a 90 hp should trim fully regardless of what prop you run.
HP at the prop is the same whether aluminum or ss prop.Your saying when new it wouldn't trim all the way with an aggressive prop.
Doesn't make sense to me

 

[WIMUSKY]

I don't have picture, but AV plate is absolutely level with bottom (lowest point of the hull).

Then it sounds like to me you could move the motor up a hole and give it a try while staying in "spec"..... Worst case scenario is you'll have to drop it back down......