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Prop question

Old 05-12-2019, 08:29 AM
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Hey, just bought a new boat, a 23 Southern Cross with 200 Suzuki on swim platform bracket. The boat felt sorta sluggish when trying to get on plane. It had a 16 x 21 Suzuki three blade prop on it. I called the guy who makes the boat and he told me to bring her over and he'd put a different prop on it for me to try. He installed a 15 x 21 on it. Took it out this past Friday with 4 on board and two large coolers loaded with beer, food and ice. Boat also has a total of 4 batteries and a trolling motor. The boat did jump up on plane a lot quicker and at WOT the rpm's were right around 5800 with a top speed of 42mph. Is that about the correct range in RPM's and speed I should be looking to get at wot? Dry weight of boat is around 2850 lbs and has a 12 degree deadrise at the stern. Absolutely know nothing about props and want to make sure I went to the right thing.
Old 05-12-2019, 09:08 AM
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Looks about right to me. WOT range for that motor should be in the 5500 to 6100 range. That's technically negative prop slip, but suzuki props are often underrated for their actual pitch.
Old 05-12-2019, 12:55 PM
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Sounds like you are close or might be there. T-top? Try checking numbers with a lighter load. Does the builder say what the top end should be.
Old 05-12-2019, 03:07 PM
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I just ran the numbers and you are at 9% slip and that is good. Gear ratio is 2.50:1 on the engine. What were your numbers with the 16" prop?
Old 05-12-2019, 03:16 PM
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Originally Posted by Hawkeye View Post
I just ran the numbers and you are at 9% slip and that is good. Gear ratio is 2.50:1 on the engine. What were your numbers with the 16" prop?
Well, that is a problem. It was still in the break-in period and didn't run her at wot with the first prop and check. Just didn't like the way it seemed sluggish out of the hole. We have a lot of shallow water around Harkers Island and I didn't like it "tail walking" out of the hole. The boat maker said that the 16 was the normal prop they put on that boat but mine is a little different with the full platform and halftower.
Old 05-12-2019, 03:56 PM
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think you should try 19 pitch and see the difference in performance
Old 05-12-2019, 03:56 PM
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Originally Posted by FatCat1 View Post
Well, that is a problem. It was still in the break-in period and didn't run her at wot with the first prop and check. Just didn't like the way it seemed sluggish out of the hole. We have a lot of shallow water around Harkers Island and I didn't like it "tail walking" out of the hole. The boat maker said that the 16 was the normal prop they put on that boat but mine is a little different with the full platform and halftower.
I was thinking a 16X20 But you are happy now right? Sounds like you had a pretty good load when you turned the 5800 and 42.
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Old 05-13-2019, 01:57 AM
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Originally Posted by Hawkeye View Post
I was thinking a 16X20 But you are happy now right? Sounds like you had a pretty good load when you turned the 5800 and 42.
Yep, pretty happy. It'll be loaded similar to that 80 percent of the time and I'd rather have it come out of the hole quicker than top end. Was just trying to make sure the numbers were in order.
Old 05-13-2019, 12:34 PM
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42 sounds pretty slow to me. That’s a really similar boat to mine. Before the trolling motor mine would hit 48, it still will light and low on fuel. I’m at a solid 45 no matter the load.

Do you have bottom paint?
Old 05-13-2019, 12:58 PM
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Originally Posted by Stevesmarsh View Post
42 sounds pretty slow to me. That’s a really similar boat to mine. Before the trolling motor mine would hit 48, it still will light and low on fuel. I’m at a solid 45 no matter the load.

Do you have bottom paint?
No bottom paint and about 60 gallons of fuel and the other load when I tested.
Old 05-21-2019, 04:04 PM
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Just propped my twin 250 Zukes and Powertech was a tremendous help. Getting my props tomorrow and hope we are right this time.
Old 05-21-2019, 05:44 PM
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Top speed is over rated for every day boating. How often do you peg the throttles and burn that gas? If you want to go for it, unload the boat, fully broken in, raise the tabs, slack tide, no wind, tilt the engine and only 15 gallons of fuel. Then see what happens.

Loaded hole shot and cruise GPH is more important to me.
Old 05-21-2019, 06:30 PM
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Originally Posted by nccoaster View Post
Top speed is over rated for every day boating. How often do you peg the throttles and burn that gas? If you want to go for it, unload the boat, fully broken in, raise the tabs, slack tide, no wind, tilt the engine and only 15 gallons of fuel. Then see what happens.

Loaded hole shot and cruise GPH is more important to me.
if he is only getting 42 on a boat that should be doing 46-47, he is probably not getting a very good cruise speed either. Mpg is also likely suffering. I still think something is amiss.

pictures of the boat and an engine height check might help
Old 05-22-2019, 03:19 AM
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Originally Posted by Stevesmarsh View Post


if he is only getting 42 on a boat that should be doing 46-47, he is probably not getting a very good cruise speed either. Mpg is also likely suffering. I still think something is amiss.

pictures of the boat and an engine height check might help


Old 05-22-2019, 04:02 AM
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I’d be willing to bet that your motor is too low. They will run much higher than you think. I have a 6” jack plate and I moved mine up 2” when installing the plate. So 2” higher in the lowest position than when mounted on the transom. I can easily run the plate up another inch or more and the boat will plane out with no cavitation. Once on plane I can run it up 3-4” without cavitation as long as I don’t make super abrupt throttle changes when accelerating.

Engine height can can be checked by running a straight edge off the bottom of the boat and leveling the engine cav plate to that. With an 18” setback bracket I would want to start 2.5-3” above the bottom of the boat.

Also, how much trim are you using when reaching your top speed? You should be at least 1/2 through your trim range. If you can’t do that without porpoising you may need a 4 blade prop.

when looking at performance reports of boats similar to yours, they are all getting 47+ and running 15x21 16x21 16x21.5 props. That inch of prop will cost a little speed but it shouldn’t be that drastic. I understand the desire for better holeshot.

Last edited by Stevesmarsh; 05-22-2019 at 04:11 AM.
Old 05-22-2019, 04:06 AM
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5800 RPM with a fully loaded boat is pretty good, regardless of what the speed is.
Old 05-22-2019, 04:13 AM
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Originally Posted by FatCat1 View Post
That's a really nice looking boat. Where are they built?
Old 05-22-2019, 04:44 AM
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Originally Posted by NC_Native View Post
That's a really nice looking boat. Where are they built?
Carolina Yachts in Jarret Bay Industrial park and thanks.
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Old 05-22-2019, 06:01 PM
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Beautiful boat and love the Zuke
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