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Got the 16' out yesterday for a good long cruise and want to report back with results of 17" prop vs. 15" prop. plus ask for more advise. Here's the set-up: 16' Classic, 20 gallons of fuel under the RPS, 300 lb. live load with Admiral sitting forward of console, max GPS speed 33.7mph at 5200RPM.

1) Max RPMs dropped to around 5200 (from 5500 plus). The stainless prop is well used and according to my marine technician it been worked-on many times. Is the 300 rpm drop the amount that would be expected when changining from a 15" prop to a 17" prop.

2) Not that I'm expecting a bass-boat take off but I wasn't at all impressed with the hole shot either. I know that w/o seeing the prop it's difficult to make any definitive statements. However, are we back to pointing fingers at the prop (for poor performance) again. Or, is this possibly the nature of this boat? I'm fine with it if it's the nature of the boat but if it's not I want to make it run the best it can.

3) Engine Height: While on plane there is a large "V" shaped spray going several feet that comes from the lower unit. The larger of the two flat plates (the plate directly above the prop) is submerged while on plane. Presently the engine is mounted where there is a 1 1/2" space between the top of the transom and the engine bracket; there is one more hole that the engine can be raised. Question: Does this sound like a case of the engine being too low? Or, Is this typical? I seem to recall another member posting a picture that showed the aforementioned plate being planely visible while on plane. My boat looked nothing like that picture.

4) The boat falls off-plane at less than 3600 RPMs (22 mph).

Thanks,
Zap

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What is the brand and size of the prop you tested?


300 rpm drop with changing the pitch sounds right but could be high. You mention the new to you prop has been "worked on". Does that mean dings repaired or re-pitched?

The measurement to look at is the anti-cavitation plate in relation to the bottom of the hull. The distance the bracket is in relation to the transom is not important.

I would estimate your motor is still too low based on the reported spray and anti-cavitation plate being submerged.

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Power Tech 36 Red is the information on the prop. As far as "worked on" I'm not positive, but I assumed that he meant the the amount of work has altered it's shape enough so that it is not shaped as it was originally designed to be. There are still some very small nicks in the prop.

With the engine trimmed all the way down and depending on which surface a straight-edge is laid the large plate is about 1 1/2 - 2" above the bottom of the hull. Is the bottom of the hull the keelson and if so is it the portion that tapers out to form the transition where the hull turns upwards to become the transome? The uncertainty of where to measure from, trim of the engine.... is why I used the transome height. That is the only measurement I'm sure of.

Zap

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You might want to mention what outboard motor your boat has well as what year/model your boat is. You cannot assume everybody reading this has prior knowledge of what you have written or even remembers it if they have. With over 20,000 registered members, WC has a lot of information to keep track of.

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It probably would have been much better to add this onto the other thread you already had on this topic.
http://www.whalercentral.com/forum/vi...d_id=11681

That sounds about right for a 70hp motor..

You might let us know what bolt holes are being used.
I believe the Yamaha has 4 bolt holes.
Sounds like you need to go up another bolt hole.

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2003 70 hp Yamaha on a 16' 1970 custom classic. Bolts are located 3rd down from the top with one hole left to raise the engine.