Finally getting to the point where I need to get a prop for my "Old School" boat.

Data:

1964 Seacraft 21', approx 1800 # naked. Approx. 3900# ready to go. VDH hull.

Power...383 Stroker 350 HP. Bravo 1 - 1.65r

What size and pitch should I start with?

Thanks,

Rev 4 22p
Be neat to try good all around life for an old school hull.

What is your x-dim, and at what rpm's are you making power?

I would look into a 25" or 23" Mirage+ or rev4, if power is made around 5000 rpm's. It does not come in a 22".

If your making power at high rpms liks 6000+ or so, 19" and 21" props are more suitable. If around 5500 rpm's, try 21" - 23" props. What speed do you expect?

According to engine specs. Top rpms are from 4800 to 5200.

Not sure about x-dim?

Not sure I follow you here. Don't you know what the term x-dimmension means, or don't you know what the number is?

If the first. The x-dimmasion on your boat is the distance from the crankshaft centerline to the bottom of the hull straight in front of your drive. That distance determins how deep your propeller sits in the water. Here is an example. If your x-dim is 16 inches, your prop shaft centerline is 5.13/16 inches below the bottom. The simple reason for this is, that the distance from the input shaft centerline to the prop shaft centerline on a standard Bravo1 drive is 21.13/16". If you don't know the x-dim number, you can always measure the parralel distance from the propshaft centerline to the bottom, and just do the reverse calculation.

Yes to both of your questions...however thanks for the explanation now I know.

x factor is 14. I would think this is a mid range to upper 50's boat.

Being a newbie where do I go from here?

Well, x-factor is a tv show for starters Sorry couldn't resist All in good fun.

If your x-dim is 14, that means your prop sits low in the water at about 7½". Because of that, you will most likely see the best performance with a 3 blade prop. When the prop sits low, there is plenty of water to "bite" into, so to speak. The aforementioned Revolution4 prop is a 4 blade prop, but it usually works well on boats with deep drives too. Time to plane will in most cases be better with the 4 blade and so will mid range efficiency. Top speed will suffer though. As said, in your case, I would start out with a Mirage+. A 21" pitch as a baseline test prop. Do you have a dealer near you with some demo props? If not, give Brett from Bblades here on OSO a shout, he can sort you out with test props.

Keep us posted. Very curious to see how that boat will do with the modern props.

Good luck with it.

Thanks, I will do a post after a sea-trial....hopefully by the end of next week.

If my dealer does not come through I will give bblades a call.

I put a Mirage+ 3 blade on with a 21p. The blade was used and in good shape.

The boat had 40 gal. of fuel and just me driving. Ran it in calm water for a mile at each rpm range. Motor has less than 3 hours on it and the boat is still in primer. Used no trim in the motor or the tabs. GPS was my speed calculator.

1000 rpm = 6mph

2500 = 23.5

3000 = 29

3500 = 34

4000 = 42

One short burst to 5000 =51.

Hole shot is strong. Power on tap at any rpm range.

I am thinking as the motor loosens up and I get real paint on it, the prop might need changing. Also I need to load in a few people into the boat a see what difference that will make.

Any thoughts out there?

Great to hear the boat got in the water, congratz.

Your prop slip is a bit high at 23%. But you say that the bottom is in rough shape with the primer? Rough bottom paint ect. can increase slip, so you'll need to get the bottom nice and slick. You menitioned that your engine is setup for 5000-5200 so I would get the rest done, and load the boat up. A way to get the slip down as well, is to try a Revoloution 4 in 21". I would not put more pitch on it,though, might hurt the midrange and punch. You can always get Bblades to work your 3 blade. He has the tricks to get the slip down and the rpms up. If your 3 blade is running strong and quick out of the hole, a 4 blade might not be needed, but it is def. worth a try.
Is your speed gps speed, and is your tach precise? Just asking.