New Prop from Chad Hill

[green16]

Need help to see if my thoughts are going in the right direction. Chad Hill built me a 14.5 x 24 pitch LH prop for my 16 footer. 1. As soon as I begin to accelerate, the entire boat seems to shake. The shaking continues as she goes faster but either improves or is less noticed because of the general ride over the water. I have checked the engine mounts (as they don't have a stellar reputation for tightening things) and they seem tight.
2. Without much difficulty, and with a better hole shot than the previous prop, I got up to 5600 RPM. This is not full throttle and I was afraid to give it full throttle as previously full throttle gave me no more than 5400 RPM. I talked to Chad Hill and the engine builder Doug Smith in Lake George and when I get a smooth day and time off, I will give it full throttle and trim her out to see how high RPM's she will run. I don't have a GPS yet but I will say that it does not seem as fast by the wind in the face cheek flapping barometer.

Chad told me previously that it calculated out to a 24.5 pitch. He said he would add some cup to the prop this winter.

Better divers are looking for my original prop.

Am I going about this in the correct order?

Thanks

[boldts]

Green16,
I'm no expert in prop performance, but let me give you what I've learned over the years. You say you have a lot of vibration until the boat gets running. This sounds to me like you have a prop that is to small. The vibration is caused usually by cavitation or prop slippage. Also your 5400 + RPMs seems to be high. You can add 1" of pitch if the prop is a stainless model and add the cup that Mr. Hill says he can do for you to bring the RPMs down closer to the 5000 area. Just wondering, was this a special order prop for you? The reason I ask, you mention that the cup could be added over the winter. If I had paid the kind of dollars that most stainless props cost now a days, I wouldn't except an answer like that if the prop was not performing correctly. Is Hill going to buy you a new engine if yours blows up because it is running such high RPMs? Has Hill offered to buy the prop back and give you the option of buying a prop that either has more pitch or diameter to help fix the problem? You might even need a little more diameter and pitch together. The only other possibility that I can think of that would cause that type of vibration would be if the rubber center hub has come loose and shifted the prop off center. This is easy to check by turning the prop by hand and watching to see if there is wobble has the prop turns. You mention that most of the vibration leaves has you get the boat going, so I don't think this is your problem, but like I said, I'm not an expert. I hope this gives you some information that you can use to get your Donzi performing as she should.

Scott Boldt

[BigGrizzly]

My Ron Hill prop, Thrasher has no vibration what so ever. Something is wrong somewhere. I have had this prop on two different drives, a Volvo 270 and a Volvo 290 neithet has any vibration. My Michican wheel does a little but not the Hill.

Randy

[green16]

Thank you for replying Scott. This engine is very solid and I am told can run 6000 RPM's (not that I ever would). The high RPM capabilities of this engine is why the outdrive was upgraded to the 290 (it also allowed power trim to be added.) The prop was special ordered for me but paid for by Great Lakes Boat Repair since they lost mine. (They got a great price for it since they are a business.) Chad Hill is Ron Hill's son. He told me that the data I gave him indicated that it should be a 14x24.5 pitch. I don't think anyone is believing me (other than the original engine builder) when I tell them the capabilities of this engine/outdrive combo. He says I won't hurt the engine if at full throttle and trimmed out I am running 5600.
I still think I had a Volvo Prop 14x26 that S&S Propellers repitched to 28. Great Lakes has told me they will get things right so I hope their word is good. It all comes down to money and that is held by the owner's wife Mrs. Eaves. Peter Eaves is the owner but apparently his wife is the business manager. But I digress.

The prop diameter is 14.5 inches so I don't think it could get much larger and still fit beneath the cavitation plate (I think that is the flat surface above the prop). I am wondering if he pitches it to 25 would this reduce the vibration/cavitation? Randy C has been very helpful and I think I'll ask him what he thinks. Thanks again.
John

[green16]

Thanks Guys, I'll get back to you soon.
John Tex