jack plate

[rockey]

I have a 21 ft. fisher boat(fiberglass) that has a jack plate on it 10 inch.
How far should the center of the prop be from the bottom of the boat. The motor that is on it is a 225 merc with a low water pick up . Right now i can run 5800 rpm and only go 50 mph. Right now the center is set even with the drain plug..This was done by the place where i bought the boat. Or do i need to change my prop.?

 

[steelespike]

Re: jack plate

Please read the stickies at the top of the page and the helps at the prop store page.
We need a lot more info.Boat type/style,dry weight,year of the motor.
Height ofb the motor is usually measured by the height of the antivent plate (just above the prop) With a jack plate the antivent plate should be visable on plane.
I usually suggest raising the motor to a point just before venting becomes a problem.

 

[rockey]

Re: jack plate

hi again . I have an 1997 21ft. fisher bass boat that is fiberglass that weighs 1700 lbs dry and around 2000 lbs with me and my gear. The motor is a `1996 mercury 225 xr2 with a 14 1/4 X22 prop on it. The boat also has a 10'' jack plate on it with the water pick-up setting 2 1/2'' below the bottom of the boat.
The motor seems to struggle to power up. I was wanting to know if this is the correct prop and the proper setting for the jack plate. Thank you for your time

 

[Dhadley]

Re: jack plate

Assuming you have the 2 liter XR2 with the 2:1 ratio your slip is about 18% which is way too much. If your boat has a pad bottom with a stepped transom and considering the 10" setback, having the propshaft centered on the drain plug isn't inconceivable with the right design prop.

However, going back to the excessive slip we need to look at the prop. When you say it struggles to get on plane, explain what you mean. Does it vent and rev without going anywhere or does it stay hooked up but is slow to gain rpm? Can we assume you have made sure the motor is running right?

 

[bob johnson]

Re: jack plate

Id ask is the jack plate adjustable or fixed?

if adjustable is it hydraulic....ie can you raise and lower it while under power?

I cant visualize your boat...and we dont know if it has a pad or not yet...

but I find it hard to believe that your cavitation plate can be 6-7" above the plug!!!!!!!!!!!..even with 10" of set back.


I would think if you were lucky you could get your cav plate up to 2 " above the waterline max....

10" of set back should only get you about 1-3"" of height while at WOT.

the rest is the dynamics of your boats hull...

which i dont know much about.

I have a 10" jack on a very flat running hull....and I can only raise my motor half the height of the jacks travel..MAYBE 3" before i cavitate at WOT...

and I have the cav plate even with the hull at full down....

good luck

get back to us with the info


bob