Prop sizing

Fallguy87 · Post by **Fallguy87** » March 11th, 2018, 4:24 pm

Hey guys. I have a 28 foot 1978 santa cruz I bought last season. Everything has been totally rebuilt. But I think the props are too small for the boat and power. They are 14x 11. Any suggestions ???

bud37 · Post by **bud37** » March 11th, 2018, 4:28 pm

Welcome to the forum......I can't really say what size you need off hand, a little more info may help the guys.....what makes you think props are too small......do you have any rpm speed number /HP you could share to help the gurus.??...... :beergood:

Fallguy87 · Post by **Fallguy87** » March 12th, 2018, 8:55 am

Morning all. I have 2 rebuilt strong 302 ford's. The boat runs at 18 mph gps speed at 3600 rpm. Pretty sure from what I've read that's way to high engine speed. Gets on plane in seconds. I'm guessing.... maybe closer to 15x15???? Does anyone know what the factory was?

km1125 · Post by **km1125** » March 12th, 2018, 10:02 am

3600 doesn't really sound that high. What are the engines rated at? What was the load on the boat when you did the 18MPH cruise? What's the condition of the bottom of the boat? Where's the WOT RPM at?

How much clearance do you have from the prop tips to the hull?

Post by **waybomb** » March 12th, 2018, 12:35 pm

3600 sounds way low for a gas engine. But I have no Ford vs boat experience.
Smaller prop means more rpms. Larger prop means less rpms.

bud37 · Post by **bud37** » March 12th, 2018, 4:46 pm

My opinion , you should be going much faster than 18 mph at 3600 in a boat that size with twins, maybe 220hp each.....do you have outdrives on your boat ??....bottom is clean right??.....really if it were me, I would take the info I have to a local good prop shop and talk to them, they should be able to put you in the ballpark. There really are a lot of variables involved in this discussion.......good luck man...... :beergood:

bud37 · Post by **bud37** » March 12th, 2018, 5:01 pm

Fallguy87 wrote:Qr Bbpost Morning all. I have 2 rebuilt strong 302 ford's. The boat runs at 18 mph gps speed at 3600 rpm. Pretty sure from what I've read that's way to high engine speed. Gets on plane in seconds. I'm guessing.... maybe closer to 15x15???? Does anyone know what the factory was?

You're in luck ...found this, but is from a 1980...probably close to yours...check it out...performance data and all...... :beergood:

http://www.carveryachts.com/media/4691/ ... ruz_80.pdf

km1125 · Post by **km1125** » March 12th, 2018, 6:14 pm

bud37 wrote:Qr Bbpost
Fallguy87 wrote:Qr Bbpost Morning all. I have 2 rebuilt strong 302 ford's. The boat runs at 18 mph gps speed at 3600 rpm. Pretty sure from what I've read that's way to high engine speed. Gets on plane in seconds. I'm guessing.... maybe closer to 15x15???? Does anyone know what the factory was?

You're in luck ...found this, but is from a 1980...probably close to yours...check it out...performance data and all......

http://www.carveryachts.com/media/4691/ ... ruz_80.pdf

Good starting point, but I think a couple things are interesting.

1) ALL the engine options are specified in HP, EXCEPT the 302.

2) The 220HP and the 302 are both spec'd in the document (twice) as being 1.52:1 ratio transmissions, but in the performance data it lists 220HP engines and 1.46:1 ratio.

The OP has 14x11 and the test boat has 16x15... quite a difference.

Post by **waybomb** » March 12th, 2018, 6:34 pm

3 blade props or 4 blade props. I'm guessing this early of a vessel had 3 blade props.
Big difference between 14 x 11 and 16 x 15.
If it has 3 blade props and they are actually that small, there are other problems.

RGrew176 · Post by **RGrew176** » March 12th, 2018, 11:13 pm

May not be much help. My 81 3007 Aft Cabin with 270 Crusaders runs 18" dia by 18 pitch props 4 bladed. I am only a little bit bigger than you are. Hope it helps.

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