Possible shamrock repower

[John Kurtz]

Thinking about repowering a 1987 26 shamrock stalker. Boat weighs about 6000 lbs dry currently with a pleasure craftt 350 gas direct drive inboard. Boat will be used mostly in Arkansas but trailered to coast for some “real” fishing and diving adventures. Currently has 54 gal port and starboard fuel tanks total 108 with about 100 gal usable.
I would like to increase speed thinking of around 350 to 380 hp Cummins 6bta? Currently has a BW 1701 but will probably have to change that out as well. This is the keel drive version so I have some concerns about current shaft size and prop size with new propeller. Of course that concern is mute if we have to change shaft log size and running gear ( all can be reworked to make fit) Is this a crazy idea? I have plenty of time and a nice place to work on it. I also have a small machine shop in the rear of my shop (lathes and mill) so making pieces and parts is not an issue
Any ideas or constructive criticism would be greatly appreciated
Engine sits under the center console entire driveline is completely accessible. I can send more pictures in any one needs or wants more visuals

Topic

[Dave Morris]

Shamrocket! Pictures and Performace

Hi Tony,

I sure wish I was west coast for this repower but I appreciate your contributions for all of us elsewhere in the world.

I am repowering my 26′ Shamrock 1990 Open (Center Console) and have a refreshed 6LPA nearby I can put into it. I wonder if you have those photos you referred to above and any performance numbers to justify the “Sham Rocket” moniker?

I thank you in advance if you have them and if not thank you again for all the information on your site.

Dave

[Tony Athens]

John,

Somehow I missed this post–Sorry..

Anyway, I have repowered 2 Shamrock “Keel Drives” like yours and both turned out really well.. #1 was done using a Cummins 6BT 210 and a Velvet drive 1:1 gear ( like a ski-boat) , and the other one we used a Yanmar 6LPA 315–We called it the “Sham Rocket”.. Very fast and very smooth……………………………….Later today I post some pics when I catch my breath..

In the mean time, are you doing most of the work yourself? Sounds like you are a total hands-on guy.. On the Shamrock Rocket, we had to redo his fuel tanks as they had rotted thru from the outside in.. I think it is an inherent problem for this boat because of the way they were installed ( talked with a few guys with this issue over the years..

As to a new Drive Train– Measure the ID of the current strut and hole thru the boat ( log)… If you can handle a 1.25″ shaft, then done right using up to a 16″ diameter prop, you are good for 350-400HP with a 1:1 gear..

Tony

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Dave Morris

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