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Prop help for my Southwind on steroids

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DenDen Quote  Post ReplyReply Direct Link To This Post Topic: Prop help for my Southwind on steroids
    Posted: May-14-2024 at 2:56pm
I have a 1975 Southwind 18 I recently rebuilt the boat and the motor.
Originally it had a 307 with 225 horse and Ellis 13 x 13 propeller
The boat seems to be all original as it looks like nothing was ever damaged or replaced.
With the old 307 the boat would run 4000 RPMs and be at 40 mph.
With the new 350 that we stepped up a bit the boat easily overspeeds the motor.
When you run it up to 5000 RPMs and pull the throttle back to stop it there you’re going about 45 mph.
The only other thing I might mention is that the clearance between the propeller and the hull is about a quarter of an inch or less. And that is how it came from the factory.
I am thinking there’s someone out there that has done this before and has some recommendations
Please help


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-14-2024 at 10:58pm
Here's a picture from your "Sea water mystery" thread showing the original prop and the same clearance between the prop and strut that you have now.

So......at least you know that nothing changed with the stringer job and engine reinstallation

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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 6:32am
Den

Looking at some old threads and pictures, it seems like many of the V bottom hulls in the 70's had minimal prop clearance with a 13 inch prop

Maybe not quite as close as yours, but 3/8 or so.

TRBenj's 79 BFN comes to mind along with a handful of other boats with the same bottom design

I think you mentioned that you don't have any erosion or prop burn marks on the hull.

Maybe the blade rake on a 13 inch Acme will be more than the Ellis and give you a little more clearance.

Maybe.......maybe not

Somebody with the initials TRB should be able to give some good input Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 8:42am
The raked acme will definitely increase hull clearance if sticking with a 13” diameter. A few of the options are also available in 12.5” and may be a consideration, they perform pretty similarly. The 542 and 1210 ran very similarly on my Riviera, that’s probably the way I’d go on a SW18 as well. If your current prop is actually turning 5k at 45mph (have you confirmed those rpm with a shop tach or timing light?) then the prop would be best as a mantlepiece or candleholder. It should be holding 1:1 at those speeds, if healthy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 63 Skier Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 9:39am
Foolish question - would replacing the shaft with a maybe 1" longer one make sense, would increase clearance and looks like plenty of prop to rudder clearance now.  1/4" seems crazy close to me, I guess Tim's suggestion of dropping to 12.5" would do the same but wonder if you'll still turn close to or over 5k rpm.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 10:00am
No, excessive strut to prop clearance is detrimental to shaft longevity and performance, and also causes prop to rudder clearance issues- especially with a raked acme. Prop to strut clearance would only be increased by ~1/4” for every inch you increased the shaft length at 15° strut angle… not a good ROI. Its a better practices to keep the prop to strut clearance minimized- just enough to fit a puller in between is fine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 63 Skier Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 11:47am
Got it thanks for the explanation.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 1:27pm
Den Den

You're supposed to mention the power level your desktop dyno program came up with for your engine and probably subtract some from that if it assumes you're using a good set of headers on land. instead of marine exhaust manifolds,

350 Chevy with later Summit Vortec heads and a pretty good cam.

Like in the other thread I'll guess 310 to 320 HP.

We have a Vortec engine with about the same power that runs happily at 5000 rpm at full throttle, and with the right prop is still at about that 1 mph for every 100 rpm ratio at higher speeds.

Here's a question for you

Does the boat still run 40 mph at 4000 rpm with the "candleholder" that worked pretty well with the 225 HP OMC?

GPS speed and something like a timing light with a tach feature should give you some good numbers.

Then with good verified numbers, and knowing what you want for max rpms and cruising speed rpms, a good recommendation can be made.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DenDen Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 5:07pm
The boat performs exactly like it did with the 307. At 4000 RPMs 40 mph. That seems logical. As for the Tach, when we were timing the motor up we had a Tach on the timing light and it matched all the way up, so that’s been verified.
I’ve been talking to a fella. He’s real knowledgeable about ski boats. I won’t mention who he is but believe me he knows. Told me that the distance from the prop to strut Can be no more than the diameter of the shaft. In this case, it’s 1 inch. That’s where we are.
I had another thought, a barefoot nautique running a 454 probably has somewhere in the neighborhood of the same horsepower that I’m talking about with my 350.
I heard they were not known to be powerhouses   The hulls of the boats were originally the same so I wonder what they were using for a prop. Of course back in those days it would’ve been an old cast prop, and not a CNC. Pretty much what I’m running, but who knows.
What does anyone think of Ken‘s recommendation of 13 x 13? I guess that’s a pretty common prop.
My only other option I think is to go with the 13 x 14. And I’m afraid that might be Too Tall.
Does anybody have one of those props wants to sell it. I would really like to go on vacation with one of each.
Remember, we are talking right hand turn.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 5:58pm
I have plenty of props in the sizes you are talking that I’d be happy to sell you, but you’re out to lunch with your thought process. You could possibly step up to the 13x12.625 (474), but any further would be foolish. The 1210/542/540 range is a safer bet.

I have a little experience with props and cc v-hulls, with both big and small blocks.

I realize you think your tach is accurate but either it’s out to lunch over 4k or your prop is a flexy mess and best used as a paperweight. If both were performing correctly, you would not see 1:1 at 40 and +1000rpm at 45.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 6:23pm
Den Den

I'll have to say that I agree with Ken's 13x13 Acme 430 recommendation, oh wait I should agree, that was me in your other thread Wink

I suppose me and TRB can disagree, but click on the link below for some reading about someone's Acme 430 experience. Alan (81 Nautique) is still around here

What he was trying to do and he accomplished was a lot like you're trying to do. Tame down the rpm on a pretty powerful engine


I'll stick with my foolish recommendation but since TRB has come up in pitch to 12 5/8, I could go down in pitch to the same 12 5/8 as a second choice.. That's an Acme 474

Maybe he's got a try it before you buy it program Wink

 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 6:32pm
No acmes in that range for sale with a free trial or otherwise but we have done extensive testing on 350ci powered boats both with less hp and significantly more than being discussed here, and the 13” (430/431/425) is just too much prop and they slow down every time. The 12.625 (474/475/449) is a magical one and goes pretty fast even when it drags the rpm down below the hp peak - even compared to a 12” pitch (540/541/515) that hits the rpm target on the nose. This is on lighter/sleeker boats than a SW.

I’ve also run enough vee hull CC’s with varying engines and props to have a reasonable idea of what works best and I’ll stand by my recommendations above.

Feel free to try for yourself, no need to take my word for it.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: May-15-2024 at 10:02pm
There was a boat company in Sacramento, Keaton Boats, they built a 18' Barefoot Keaton for a while that looked a little like the early ski Nautiques.  It was also known as the Keaton Utility if you try and look it up.  
The barefoot version was built in the 1980's.  I skied with a couple of these boats.  Keaton used a bone stock 350 chevy, 260 HP.  They propped it with a 12 x 15 prop.  These boats would run 55 MPH right from the factory and pulled deep water starts with plenty of power so they were popular locally with the barefoot crowd.  The hull was a faster design than the Ski Nautique, maybe lighter than the SN.   I only mention this boat because it ran well with the 12x15 3 blade prop, thinking maybe it would give extra hull clearance but I have no idea how it would work with a Nautique SW hull.  TRBenj has offered great advice on props for many years so I would not discount the advice given.  What he shares he has actually done first hand.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DenDen Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 12:51am
I’m confused.
Let’s say forget about diameter for a minute.
And go with pitch.
A prop with an 11 pitch would be running a higher RPM and a Slower MPH than a 12 pitch of the same size. Having said that, a 13 pitch would be even Lower RPMs at the same MPH?
Working it the other way at the same RPMs say 4000.
An 11 pitch would be a lower MPH then a 13 pitch.

So I have a 13 pitch and I’m running too high of an RPM. Why would I want to go to a lower pitch that would run yet higher RPM?
In terms that I would understand, I want to shift gears up, not down.
That is why I’m confused
Or quite possibly I am just dense.
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I have not figured out those damn emojis
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 2:04am
I think the basics are, the first number, 12 or 13 is the diameter of the prop, second number is the pitch but I was told it is how many inches of travel through the water with one rotation.  12 x 15 = 12" diameter x 15 = 15" travel per rotation.  Less pitch = more RPM, so a 12 pitch will spin more RPM than a 15 pitch.  

In addition to this the type prop, number of blades and the cup type all come in to plan to get the perfect prop for your boat.  There is more to it and others can offer that information.

The 13x13 prop was pretty standard on the older Nautiques but in my 1978 Nautique with a strong 351W engine I ran a 13x14 and was very happy with it.  50+ MPH and still performed well pulling up skiers.  A modern CNC prop could probably have done even much better than my old 13x14 prop as technology improved for props over the past 40 years.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 5:59am
As I keep saying, your prop is junk if it’s actually spinning 5000 at 45mph on that hull- it should be holding 1:1 speed vs rpm, and if it’s not, it’s flexing rather than moving the boat forward faster. Throw that data point in the trash when comparing to other props.

The modern acmes have a lot more blade surface area than the hand finished 60’s designs like you have. Dropping 1” of pitch is typical to get the same speed vs rpm characteristics.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 7:54am

Yes seems Den is not yet privy that 12p acme is very much 1mph/100rpm like all other brands 13p.
Den an acme 12.65p is going to be more prop than you have now, even if it wasn't suspect.
a 13p acme is like a 14p other brands, both are too much bite. one needs a big block or stroker sb to spin that best.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote fanofccfan Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 8:07am
I have purchased several props from TRB over the past few years and not once have I had one ounce of regret.  He has done the research and has the data to back it up.  I also thought my RPM guages were fairly accurate and in every instance they were not.  He insisted I get good numbers and in the end it proved to be worth the effort.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fanofccfan Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 8:09am
I forgot to add to the above post that the new CNC props wake up old boats in ways I never thought possible.  Noticeable and favorable differences for sure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 63 Skier Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 9:23am
Originally posted by fanofccfan fanofccfan wrote:

I forgot to add to the above post that the new CNC props wake up old boats in ways I never thought possible.  Noticeable and favorable differences for sure.

Yes to this!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeinNY Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 11:24am
Certainly- the vortec 350 can get to stock bbc hp numbers pretty easily just not at the same rpm - which is why you wouldn’t want to run the same propeller - good advice above.   The ellis prop is a bit of an unknown,   Tunneldrive hull guys purportedly love them to reduce vibrations which could be a cupping thing - in my experience cupped props are even more useless at higher rpm’s than lower rpm’s.

Either way don’t fear the rpm I wouldn’t prop that boat for anything that it can’t spin at least 4900 rpm - assuming the cam is healthier than a stock excalibur grind i’d probably be shooting for 5100 rpm plus
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 1:16pm
Kinda funny what a phone call can tell you.

Talking to Den, the boat runs great for him with the Ellis paperweight, flexy mess, junk prop and it revs to some unknown rpm because he backs off as he's getting to 5000 rpm and what it'll do a 5000 isn't really 45 mph but still climbing some. 

The tach compares well with his timing light with a built in tach feature. The GPS is from a phone app so somebody will probably question that reading.

When he's out again he'll get some numbers above 40 mph, like when he's at 4500 rpm what's his speed and work his way up from there with some more numbers.

He's not sure how high it will rev cause he backs off at 5000 or so and doesn't want to run it higher than that. 

Maybe next time he let's junior drive and they see what it'll rev to, maybe not.

So more numbers to come in the future.

Now speaking of Ellis props, I went to the garage and pulled out my Ellis 13X13 and we put it on a friends mid 70's SN this morning.

The boat has an Acme 540 on it so we got some numbers and it ran at pretty much 1 mph per 100 rpm.

It would do 45 at a little over 4700 rpm like it has since the prop was put on it.

Quick prop swap.............. and get some numbers for the flexy junk paperweight.

Ran at pretty much the same 1mph per 100 rpm, but it was running roughly 100 rpm lower for the same speed.

Full throttle it went 46 mph at about 4600 rpm.

Our "butt dynos" both agreed that the Acme was better accelerating, racier feeling and the better all around prop for his use.

I remember the same outcome a number of years ago on my mid 70's SN, but memory can be a funny thing, so the morning check was to verify things instead of relying on the memory.

So, the paperweight was faster, imagine that Wink That's a known phenomenon

Sometimes the junk/ flexy mess/ paperweight is OK.

Same boat, same tach and same GPS speedometer about 45 minutes apart


 

I offered to send it to DenDen so he could compare for getting some "baseline" readings but for now he's gonna get his numbers mentioned above.

And in case anybody's wondering I like the Acmes that we have on a couple of boats and a couple of others have flexy junk paperweights that serve me just fine too and if I'm buying something new, it's an Acme or OJ CNC prop.

So let Den Den get some good accurate numbers, but he's hellbent on reducing his rpms from what they are now.





 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fanofccfan Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 1:52pm
Nice work Ken!  Did you lap the props when you switched them?  If not then I am not so sure the data is reliable!  (that is meant to be a funny by the way)  Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 2:00pm
Originally posted by fanofccfan fanofccfan wrote:

Nice work Ken!  Did you lap the props when you switched them?  If not then I am not so sure the data is reliable!  (that is meant to be a funny by the way)  Wink

OK DBB............that's good for my chuckle for the day, maybe the week, maybe longer.

Better watch it, I just checked, I still have that picture of you sitting on a trash can driving the Mex Nautique. One of my favorite CCF pictures with that big smile Wink

I wonder what that boat had for a prop after seeing the other pictures of the boat
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeinNY Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 2:26pm
There’s no doubt that the smaller bladed cast/hand worked props are often faster than an acme or cnc OJ - particularly on a smaller/lighter older boat like mustangs/skiers and ski nautiques older than the 2001’s.   They have less drag and often help bring up the nose. The only boat i have ion the water today is rocking a federal - but it sure does take the joy out of really hammering on it - can’t throw $450, or multiple 450s at everything in the barn .

I’ve spent the equivalent of a pretty good modern wakeboard boat rebuilding small blocks on steroids - all the best steroids - that I have broken messing around for more speed- it was usually props that were just a bit too big, or brought down the rpm a bit too much that broke them.   More rpm - less load, less stress - less heat- less detonation- less pieces of metal in the bilge.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 2:37pm
I concur with Joe, let them spin, more rippems the better.. Low 5's on an engine with lungs is right there
higher vacuum when cruising. better throttle response, less strain per power pulse
a little spicy with one aboard, means perfect when loaded up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 2:53pm
To clarify, not every hand finished prop is a flexy paperweight- just the ones that run away up top. Can lend you one ken, if you want it!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DenDen Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 3:19pm
How about some boat pictures?

















photo uploading sites
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-16-2024 at 7:14pm
Boy, look at all the activity on this thread now

I would have posted something earlier, but I was dealing with some anger management issues.

I had an angry prop that didn't want to go back into storage.

After a long conversation that I really shouldn't post here, she (Ellie is her name for obvious reasons) was happy again knowing that she still had it compared to those hot looking new young props and once she got going .......well you read it above.....she was as good as they were

That  finally calmed her down and I got her all ready for a nap

Here she is all dressed up do do double duty 

And Bill............I didn't lap the candle to the shaft, I hope nobody minds  Wink









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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: May-17-2024 at 6:14am
OK Den

Now that you've been told why something like the 13x13 Acme I recommended is apparently too much prop for your application, i should probably explain my thought process.

I figure your boat is a v bottom, roughly 2400 ish pounds, roughly 320 HP  from a SBC (your desktop dyno said a little more)

Then I say to myself "do I know someone with a v bottom boat inboard with the same power from a SBC with an Acme prop on it.

After some thought, I say to myself......of course you do.

It belongs to one of my kids.

We'll call it brand "X" or maybe brand "S". 315 HP @5000 rpm SBC, it's a little porkier at about 3000 pounds

Being familiar with the bottom design of your hull not much difference in the bottoms.

Now what prop do we have on that boat I ask myself

It should work for Den's purposes.

It's a 13x12 5/8 Acme and the boat runs at 5000 rpm, 50 ish mph. As far as acceleration, we'll just say "no problems in that department" .

I'd lend you the spare prop for a trial run. but your boat would go backwards because it's a LH rotation Acme 449 and it fits  a 1 1/8 inch shaft so it would be kind sloppy in the fit department. Wink

I think TRB called it a magical prop earlier in this thread. We'll agree on that

Wanting to keep the rpms down with potentially more power and 500 or so pounds less weight, and similar hull bottoms, I figured the 13x13 RH Acme 430 would be good for you and you'd be in the high 4000 to maybe 5000 range Second choice mentioned above was the13x12 5/8 Acme 474 (the RH version of the magical 449 but for a 1 inch shaft like Den has)

So, imagine that, I have some prop experience, something similar to base the recommendation on and toss that out there.

It seems like based on some of the above comments, It's a terrible choice and a SBC just can't handle that prop.

Anybody can feel free to tell me where my logic is screwed up Wink


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