1970 Merc 500 Thunderbolt on a 15 foot Mirrocraft. What pitch prop?

I have a 1970's Mirrocraft Titan 15. You can see the boat specs on the attached photo. Weight, length etc.

Boat has a 1970 Merc 500 Thunderbolt 50HP. How would I go about selecting the pitch that would be best suited for this boat?

When I bought the boat it has a Michigan Wheel 10 1/4 x 13 prop on it. Obviously this was not the prop that came from the factory. Runs good, no complaints. Does about 25~30 mph. Unfortunately I broke my prop. I need to get another prop and all I can find that is a directly replacement locally is a 10 1/4 x 11 and a 10 1/4 x 12 pitch.

Hell I don't even know if the 13 pitch was right for this boat to begin with. Unfortunately I have no RPM gauge so I don't really now what it ever ran at.

I'm curious to hear what some of you guys who understand this stuff think the pitch SHOULD have been for this setup based on the weight and length etc.

​Thanks!

Buy a tach! Important.

Jeff

Suggest a tach!

Don't even know what to buy.

Also it's my understanding that the plug that is capped off on the front of my Mercontrol unit is FOR an RPM gauge. Does this supply gauge power too? How would I find the pig tail that goes there? I checked eBay but either searched wrong or there are none on eBay.

Awesome diagram! That will be helpful for my harness rebuild too! I'm going to strip down my harness and replacing ALL of the wiring in it over the winter. It's brittle and cracking.

Now I just need to find a harness plug that will fit it, I would rather not open up the MerControl. Certainly will make wiring a TACH easier!

I bought a 10 1/4 x 12 prop simply because I got a REALLY good deal on a brand new in the box Michigan Wheel prop. They were discontinued back in like 1996 and hard to find. The shop that had them was just trying to clearance them out cheap.

I have a new Michigan Wheel 10 1/4 x 13 too which is what was on the boat. The reason for this prop is just as a spare as bent a prop about a month ago and broke a blade off another this past weekend so a 12 pitch prop as a backup is better than nothing! I sometimes take my boat 20+ miles up or down river.

Yeah so this last weekend I snapped a blade off my prop on a stump, I had to go over 10 minutes with 2 of 3 blades to get back to the launch. Hopefully I didn't mess anything up in the engine but it ran the whole time. The vibration was bad though!

Anyway I have two props now, my primary and a backup and I think I will add a tach. Just not sure which to buy yet.