Way back in late 2007, when we first started this refit, the boat was outfitted with Super SeaMaster marine engines, turbocharged and intercooled Ford Super Duty 534ci early 1970’s monsters that developed 400hp at 3200rpm. All that power was pushed through 1-1/2″ Aquamet 17 shafts (see the Parts For Sale page if interested!) to a set of 3-blade props. After repowering the boat to Cummins 450 Diamonds in 2012, which came with 1.5:1 gears, and finally installing the new 1-3/4″ Aquamet 22 shafts, it’s always been a big question what size of props would work best. I can only estimate the weight of the boat when she’s done. A buddy of mine — and Roamer guru extraordinaire — has manufacturer’s data indicating that my boat should weigh in at around 32,000 pounds. But other Roamer 46s I’ve heard about range up to 50,000 in aluminum and 55,000 pounds in steel (with Detroit 871 power that weighs 2x the mass of my Cummins). So I checked with Miller’s Island Propellers and, what do you know…the ol’ 3-blades just might be perfect for this HP rating gears, assuming the weight comes in around 37,000 pounds. In any case, they’ll work fine as the sea trial props to give me a baseline.
First, some stripper had to do its work
I’d barrier-coated and bottom painted the props way back in 2008, since the plan then was to splash the boat and continue the refit at the old marina where we’d found her, and that marina’s got a serious fouling problem. Plans changed, so all of the coatings had to come off before going to the prop shop.
They cleaned up pretty good!
Back from the prop shop, bored out to 1-3/4″, balanced, and polished!
In the pic above, the props are installed loose on the shafts. I won’t permanently install them until I have a chance to test the fit with Prussian Blue and lap them with valve grinding compound if necessary. I’m also waiting on a 2″ socket wrench so I can torque them down. Stay tuned…
Next up on our 1969 Chris Craft Roamer 46 Refit: Installing the Props
1969chriscraftroamer46 
Great to see those shining props.
You may already know all of this but here goes. When you sea trial do it with full fuel and water and make absolutely sure you have a digital phototachometer to get accurate RPMs. I recently got one for $30 online. Measure your RPMs at wide open throttle (WOT) in gear and out of gear (high idle). Don’t worry about over-revving the motor in neutral–it cannot be done. Your high idle RPM should be between 2920 and 3020. If it is not, adjust your throttle linkage so you get maximum travel and when you get your high idle in the correct range, run the boat again to get your real WOT in gear. Next, take that number to your prop shop and tell them you want to adjust your props so you can get 2750 RPM. This is the recommendation of experts and is ABOVE the rated RPM of 2600. This is a really solid engine, but propping only to 2600 or below has historically resulted in dropped valves.
Let us know when you go to design the exhaust mixer. There are important lessons there and since you are making all of this from scratch you might as well get it right the first time.
Thanks, Jay!
I’ve got the phototach ready to go! On the exhaust, I’ve got my google sketchup model ready to build out the mixer. I plan to take it as high as the hard insulated dry stack can go, then tip it over and point it toward the muffler (showerhead on the down-side). DeAngelo has already given me the quote, but I can’t finalize the dimensions and angles until the engines are in their final position. Which couldn’t happen until the props were on. Which couldn’t happen until…you get the idea.
I look forward to your input when I post the sketchup renderings of the exhaust riser!
Cheers
Q
So what are the dimensions of the 3 blades? Pitch and Dia?
Cupped or non cupped?
mark
Sundowner 41 Regal w/ cat 3126’s
24 x 22, no cup.