208 with 200 HPDI ( Engine Height )

[Captnobs]

Greetings,

I am a new to this site and a proud owner of a 1997 208 with a Yamaha 175. I will be mounting a 200 HPDI and was curious as to what hole others have used with this combination. Currently, the 175 is mounted using the lowest hole. The cavitation plate is level with the hull but it appears buried when on plane.

I had another boat with the engine also mounted using the lowest hole. I was able to raise that motor 2 holes which increased performance significantly without any cavitation.

Thanks,
CaptNobs

 

[Pay2Play]

I have a 208 with a 200SWS, boat has a hardtop. Originally the motor was on the lowest hole...I raised it 2 holes, but the performance was not that much better for me. In fact I plan on dropping it back at least one. I've tried diff pitch, 4 blades and feel I have better handling overall at the lower height.

 

[Curmudgeon]

The cavitation plate is level with the hull but it appears buried when on plane.

'Level with the hull' is a rule of thumb for a starting point, only, and you now see why. Raise it up at least two holes and see where it is. The plate should be 'slightly' above the water, but still getting splashed. If it blows out on tight turns (at speed), drop it a hole ... :wink:

 

[Captnobs]

Thanks for the reply... I am hoping someone else has the same setup. I am still unsure, 1 or 2. Too high, I lose a weekend pulling & re-calking. Too low, I wait until next season.

 

[Britfish]

happy to send you pics of my set up - need email address

 

[Tucker]

Think there is a design deficiency with some Grady's. My cav plates are level with the hull but the prop is buried when on plane. With twins, If I raise a notch I get blow out in the turns. Been thinking about 4-blade props.

 

[seasick]

Think there is a design deficiency with some Grady's. My cav plates are level with the hull but the prop is buried when on plane. With twins, If I raise a notch I get blow out in the turns. Been thinking about 4-blade props.

You can't use the general guideline for a single on twins. There are more factors to take into account. You can see that depending on motor spacing and dead rise angle, it can be a lot easier for a prop to raise too high when the hull is not parallel to the water as is the case in a turn. In those cases, the motors would be positioned lower than for a single motor of the same model.

The position of the prop in the water also depends on trim and bow angle which can be affected by load etc. The point is that there is no one perfect position. There are settings that work better given a set of conditions.
I always laugh when someone states where the cavitation plate is at speed on smaller hulls since in order to look at it, you have to move aft and look over the transom. That changes the trim angle and whatever is noted may not be the same when sitting at the helm

Trim tabs can make a big difference too. Thay can reduce roll which may reduce blowout and thay can change the cavitation plate orientation.
I think that calculating slip over various speeds/revs and conditions can help identify areas of concern. Using the 'which hole do I use on the motor?' is not really all that scientific.

 

[Captnobs]

I swapped the motors and mounted the 200 HPDI raising it 2 holes (third hole) with a 17P prop. So far so good. On a clam day with a full tank of gas, trimmed up, no blowout/ventilation issues. I am getting WOT 5400 RPM.