1969 Glastron 115 HP Electronic Shift Prop Selection

[shanman]

I have a 1969 Glastron V176 with a Johnson 115 HP outboard with electronic shift. I currently fish above 9000 ft in elevation with a 15" prop and I have no power without bogging. I heard to switch to an 11" prop because of the elevation. Can I buy any 11" prop for a Johnson outboard or do I need a specific prop for the electronic shift and for that particular year? Parts are hard to find and specify for pre 1973 Glastron boats... Thanks!

 

[jimmbo]

Welcome to iboats
First of all, what WOT RPMs are you getting with the 15" prop? That engines' WOT range is 4500 - 5500. The altitude is going to kill your power considerably, even propped in the upper half of the range. Also your carbs will be running rich, you can adjust the low speed mix, but setting 4 carbs is no fun. The high speed jets are fixed and I don't believe OMC ever offered 'Altitude' jetting.
BTW, it is not Electronic Shift. It is what's called Hydro-Electric Shift. Electric solenoids direct oil to move the shift mechanism. A well engineered system that works well if the oil is kept clean and water free. Specific props are not required by the shifting method. Parts for what is almost a 50 yr old engine are getting harder to find, but a lot are available.
The bogging... when was the last time the engine had new plugs, carb cleaning, link and sync? Dirty/misadjusted carbs and synchronization are the main causes of bogging on acceleration.

 

[Texasmark]

Besides rejetting, I think the number the big guns on here used to use was 1" drop in pitch per 1k ft of altitude. So 11 vs 15 is better but not where they said. Thinking about it, as I recall altitude chamber testing during survival training, above 10k you need pressurized assistance for the human body. Don't expect much out of your boat at 9k..