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

https://ibb.co/SwScnTF" rel="nofollow">

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 

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

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.

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 

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

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=19839&title=new-acme-430-prop-report" rel="nofollow - link

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 

 

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.  

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.

Yes seems Den is not yet privy that 12p acme is very much 1mph/100rpm like all other brands 13p.

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.

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!!!

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  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

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https://ibb.co/ChHK9Sb" rel="nofollow">  

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.

 

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 

I wonder what that boat had for a prop after seeing the other pictures of the boat

higher vacuum when cruising. better throttle response, less strain per power pulse

a little spicy with one aboard, means perfect when loaded up.

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  

https://ibb.co/ydq2WYb" rel="nofollow">

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. 

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 

What Joe was trying to say was, don't plan on any adjustments to the prop.  Buy a CNC per the advice above and run it.  By running it and then "adjusting" you'll end up with worse performance than by simply running a correctly sized prop.

I found when I was first reading about modern props that the couple of rules I thought I knew about props were out the window.  I think in the past people would do a bunch of trial and error, bring their prop in for more cup or to cut down the diameter as you are talking about, but they were adjusting a prop that was perhaps adequately designed but not precise, so maybe the adjustments would help performance because the base product wasn't all that great to start with.

He wanted to drop his full throttle rpms down to around 4500, so after getting some input here and from various other places he got a new Acme 13x14 from Delta propeller on their recommendation (with one free rework if needed) and got some new baseline numbers you could say.

Same tach and GPS as before, he had some new numbers 35 mph at 3000 rpm, 45 mph at 4000 rpm and 49 mph at 42 to 4300 rpm and plenty of acceleration

He's sorta happy but he'd be happier at 4500 or maybe a little higher rpm.

I "gently" reminded him that nobody here had recommended that prop saying it was too much prop and would do just what it did.

I'm sure he'll update with his next step which will involve talking to Delta about picking up about 3 to 500 rpm. whether it's with a prop swap or a rework of what he has now

Just to repeat it again, he wants to stay at or a little above 4500 rpm at full throttle.

Myself, I think the answer was in the thread, but that's how you learn, get a bunch of input then take your best shot and go from there  

In the meantime, I think he may be on vacation enjoying some cruisin' in his boat (or will be soon)

I think it was the mother as the story goes. 

Looks like you're trying for 5000 ish  now like was mentioned plenty in this thread instead of 4500 ..........sounds like a good plan to me anyways 

I think you missed one Den 

Get that thing in the water and do some enjoying.

63 Skier said it well