What's with the gearcase dimension that ...

[Boomyal]

...I see listed when looking at certain propellers? I think a 4 /34" gear case was one that was mentioned. What is this dimension for? and how does it affect a prop that you might buy?

Another thing that bugs me is that I have run across several used props that look like they might be suitable except they do not always give the diameter, only the pitch. They do give the brand and a model number but invariably a google search for that number turns up nothing. A couple that come to mind were Merc brand props. one in particular was a 48-65992-21. I could not find a listing or full specs for it anywhere.

 

[Frank Acampora]

Re: What's with the gearcase dimension that ...

There is a whole slew of 13 inch diameter propellers. Newer Mercs and OMCs of 100 HP and more have the 4 3/4 inch gearcase. This means that the diameter of the gearcase is about 4 3/4 inches and the hub of the prop needs to be equal to that to prevent exhaust from blowing out over the prop and fouling the blades. Force engines and some of the smaller Mercs around 90 HP use a 13 inch diameter prop with the same 15 spline pattern but have a 4 1/4 inch diameter gearcase. The props for larger Mercs will not fit these. SO: You need to be careful when buyiong a prop, especially private sales.

 

[Texasmark]

Re: What's with the gearcase dimension that ...

There is a whole slew of 13 inch diameter propellers. Newer Mercs and OMCs of 100 HP and more have the 4 3/4 inch gearcase. This means that the diameter of the gearcase is about 4 3/4 inches and the hub of the prop needs to be equal to that to prevent exhaust from blowing out over the prop and fouling the blades. Force engines and some of the smaller Mercs around 90 HP use a 13 inch diameter prop with the same 15 spline pattern but have a 4 1/4 inch diameter gearcase. The props for larger Mercs will not fit these. SO: You need to be careful when buyiong a prop, especially private sales.

Agree. However your XR6 as I recall is setup for running light boats fast meaning that even though it is 150 hp, it turns a smaller diameter prop faster with it's 1.87:1.

Measure the diameter of your gear housing. As Frank said if large it will run props in the 14" diameter variants or if the smaller diameter it will only run the 13" variants. I ran a 14 1/4 on my 4 1/4 (small) gearbox on my 90 once just to do it. It cleared my AV plate by 1/4" and I had to notch my trim tab. I had to make a sleeve to set it back from the gearhousing as the outer hub was the same diameter as the housing rather than fit into it like the standard 13" dia props with a smaller barrel diameter did.

Mark

 

[Boomyal]

Re: What's with the gearcase dimension that ...

Hey, Mark, where in Texas are you? My Daughter and her husband just moved to Lubbock. They just arrived from Kutztown PA. She got a great job at Texas Tech. She did a summer internship there about two years ago and just loved the people and the Texas schtick.

btw, my unit is an MR1 outdrive. I've been looking for a used 15 1/4 x 21 prop. It is what the book called for for that motor/drive combo and the boat length and weight. I have no use history with this boat and I think it came with various shaved down/repaired props. I want to get what the book calls for to establish a baseline.

 

[Texasmark]

Re: What's with the gearcase dimension that ...

Can't help you on the prop. On TT and Lubbock, my sis and BIL graduated from there. I live N. of Dallas.

Welcome to the great state of Texas.

Mark

 

[jestor68]

Re: What's with the gearcase dimension that ...

There is a used Michigan SS 15-1/4 X 21 prop listed on E-Bay for $75.