Planing issue, looking for direction.

Hello, I currently have a Wellcraft 218 Coastal 1995 model, this boat seems to be an anomoly, as it is powered by a v6 Mercruiser, w/ an alpha drive. The engine is mounted in a box, above the water line, and the outdrive is basically hanging in the air. I am looking for some input to solve getting the boat on plane. The boat will not get on plane, motor will lug all the way to 3800 rpm, and never break plane. Although if I perform a quick "s" turn, she will jump up and run to 4600 rpm with a 19" S/S three blade prop. It seems the drive is mounted too high, as such minor, trim adjustments, 1st 2" on trim cylinders, cause cavitation. I am considering a large 12x12 tab set, or possibly extending the hull under the engine box. The transom design seems as if Wellcraft placed an I/o on a boat specifically designed as an outboard with a euro style transom. Any input would be appreciated.
Thank you to all in advance.

 

If this is a factory produced boat then I would assume that it planed properly when it was built.
1. Check with the builder if you have the correct prop on the boat. It sounds like the prop is totally killing the engine by having too much pitch. Try and experiment with a lower pitched prop.

2. Was a large amount of weight added to the boat? With a fixed amount of horsepower, the heavier you are the slower you go, up to the point where you cant get on to the plane.

3. What condition is the engine in? Is it down on power? Running on 5 cylinders? etc etc.

4. Can you post a profile of the boat showing the bottom at the transom, so that the outdrive is visible.
regards
FXLiebenberg

 

More Clarificatons on planing issue

Thank you for responding, this is a factory boat, although no records in their catalog show such configuration. The boat with a 200HP O/B, says plane in 3 mins., with top speed of 45-49, and cruise of 35mph, using a 17" s/s prop. I have tries a 16x16 dog-eared prop to no avail, the engine has 2 hours on a new long block, according to the prior owner it performs better than it did before.

 

That size boat with a V6 should use a 15 or 13 pitch prop. 19 is overpropped and won't allow the engine to develop the proper RPMs.

 

The 19' Pitch current prop does allow 4500 WOT operation when on plane and trimmed out. When using a 16x16 Prop the rpm range was well beyond factory specified. I am possibly looking to try a 4-blade 18" pitch prop.
Thank you

 

I understood it was doing 3800 RPM with a 19"