Boat Plane issue

[Wee_Isle]

Heya Guys I have a 87 250da powered by a 350 CID motor and a OMC cobra drive. I had 10 people on it and couldn't get it on a plane even at WOT....in the near future I would randomly like to pull a tube or two. I don't know the oem prop size, just yet.

How can I prevent this in the future?
should I get a four bladed prop?
Is this a gearing ratio issues? or lack of power?

 

[JimT]

Did you have the trim tabs set all the way down?

You can also try moving some people forward to keep the bow down when accelerating.

It may be that you are just too heavy to get on plane with that many people.

 

[Presentation]

Get a bigger boat with a larger motor or take fewer passengers.

You are really asking your boat to do too much.

It’s possible you may get on plane with 10 light people, forward bias of passengers, drive and tabs lowered, low fuel, no water, and minimal gear onboard, a freshly tuned engine (new plugs, wires, rotor & cap) clean hull and a low pitch propeller like a 3 blade 17 pitch prop.

 

[tdbuk]

I have a performance issue of my own that hopefully someone can help with. My 1993 220 overnighter has a 5.7 Mercruiser and seems to be underpowered. With 4 people it takes a while to plane out and with 6 people you have to move some weight to the front to get the nose down. Is this normal for this boat/motor combination?
I just got the boat and wasn't expecting speed boat performance but was figuring 4 people and a skier wouldn't be out of the question. With the current performance I wouldn't want to be the skier. Top end speed with 4 people is about 30 MPH at about 3500 RPM measured using a GPS. Anybody have any insight for me. Thanks.

 

[JVM225]

I have a performance issue of my own that hopefully someone can help with. My 1993 220 overnighter has a 5.7 Mercruiser and seems to be underpowered. With 4 people it takes a while to plane out and with 6 people you have to move some weight to the front to get the nose down. Is this normal for this boat/motor combination?
I just got the boat and wasn't expecting speed boat performance but was figuring 4 people and a skier wouldn't be out of the question. With the current performance I wouldn't want to be the skier. Top end speed with 4 people is about 30 MPH at about 3500 RPM measured using a GPS. Anybody have any insight for me. Thanks.

It could be a prop issue. RPM is way low for that motor. I don't know exactly what it should be, but believe it should be in the 4400 - 4600 range at WOT.
The boat should plane out with no problem with 4 people aboard.
Maybe a larger diameter prop with a lower number on the pitch.
Call a prop guy (google prop gods and/or propdoc) for advice.
They will want to know what you have on there now. It (diameter & pitch) should be on the prop itself.
You would be surprised at the difference a prop will make in a boat's performance.

 

[Sorrento Dude]

Wee Isle.

I also have a 87 250da with the 260hp 350, but i have the
alpha 1. With 10 people on board you are maxed out. I believe that the boat is under powered in the first place. I had 5 people on my boat and i was fully loaded and it took awhile to get to plane. I am also running a 3 bade aluminum 15x17 prop.

 

[tdbuk]

Thanks for the reply. I checked the prop size versus the sea ray recommendations here http://www.searay.com/boat_graphics/electronic_brochure/Company1729/1C1_25_74DEIP4PX0O.pdf and I believe I have the recommended 14x19.

One thing to note is I do not believe this is the factory engine so I may have the Alpha One drive for a 5.0 or 4.3L which would be a drive ratio of 1.65 or 1.84:1 vs 1.5:1 for a 5.7L. How would this impact performance? I would think this would give me better take off. Is there any way for me to check this?