UPDATED: I had a feeling I was over-propped...

[Philster]

I have a 26' 1996 Scarab. 25 pitch prop. I bought it this past fall and love it, but I had a feeling it was overpropped, just from reading about props here and doing some math. I could never come up with an answer that was recommending anything bigger than a 24 pitch. Based on power, weight, gearing I was always getting 23p or 24p. Mostly 23p.

Well, she's been out twice, and she makes 4400 to 4500 RPM at WOT. I got her to 60 (barely). She does 57-58 easily and she is at a wall at about 4400 RPM or a little more. Well... maybe she has other issues, right? Nope. She was surveyed and checked out on all fronts. Good compression. All good.

Maybe.. MAYBE I could have leaned on her longer, but she was at a wall. One run was totally flat water... and one was light chop.


I have a feeling anyway about the prop... Then I find two things that scream 'too much prop'!

First is a video of my identical boat doing 64. The video shows the tach and speedo and conditions. At 5000 RPM, she is at 64 MPH.
http://www.youtube.com/watch?v=H6iIq4WWugQ&NR=1

Then I find the factory spec sheet via Wellcraft: She came with a 23-pitch prop. She did 61 at 4800 RPM as the advertised test speed identically equipped (except for the prop).

I'm looking for a modern, 23p prop. Off I go!

 

[QC]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Dude . . . like wow, you didn't need a Welcraft spec sheet to know you were overpropped. Your "Merc" spec for WOT RPM is 4600-5000. No matter what Welcraft or prop calculators tell you this is the ultimate spec period.

 

[45Auto]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

LMAO - That's what I really love about these forums - the way so many people live in dream land!

I take it you traded the Scarab you had in this post last month that was doing 65 MPH at 5100 RPM with the 25" prop for the dog you're talking about now that will only do 60 MPH at 4500 RPM?

Post #11 on this thread, dated May 18:

http://forums.iboats.com/showthread.php?t=396694&highlight=lockheed

63-65 MPH @ 5100 RPM w/ 25p SS Mirage prop; 502 Cubic Inch (8.2 Liter) Merc/Bravo 1, on a Scarab deep-V hull with 23 degrees of deadrise.

Don't you just love it when they can't keep their fantasies straight!!!

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

As explained, that's what she'd do propped properly, so there is no fantasy. And whose fantasy involved 3 MPH? I even made fun of the PO for thinking she was a 70 MPH boat.

I have the wrong prop, so you can change the specs to read the same with a 23p prop. That's all that needs to be tweaked.

Why don't you watch the video of the same boat equipped bone stock and tell me if my numbers are off. It's a 63-64 MPH boat at 5000 RPM.

What is the big deal? To get that it needs to be propped right @ 23p confirmed by Wellcraft. What, you're gonna make me out to be some bragger? I didn't walk in anywhere and brag up that it's a 70 MPH boat.

It a low 60's (61-65) propped correctly and not a high 60's boat (66-69) boat and that is what I posted.

Sounds like you have a problem with something. Why so bitter? I don't get the hostility. I somehow lied about a Scarab 26 and created a "fantasy" that it is a 63/64 MPH boat? Wow. Just... WOW.

It's getting a 23p prop and I doubt anyone on this forum would say that won't put my into the range quoted!

 

[QC]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Relax guys . . .

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Relaxed here. I don't like the tone that was taken with me. I did a pretty good assessment of the prop vs. speed vs. RPM and get treated like some speed fantasy guy. Jeeze, I nailed it to within 1 MPH and I live in a fantasy world.

 

[45Auto]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Wow, sorry dude!

I just found it funny that a month ago it was turning a 25" pitch prop at 5100 RPM, and now it'll only do 4500 RPM with the same prop. You typed it, not me. Didn't see anywhere in your original post that it wasn't your boat you were making the speed claims for. Don't worry about it, it's the internet, anybody can claim anything they want!

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Whether is goes 63 with a 25p or 23p, it's a boat/engine/drive with that capability, and there is video proof of it, so I am not getting the issue here.

When someone passes me, I don't care what prop he has (although he might).

If I were taking delivery of a boat and posted it specs, and when it got here it had the wrong prop that held it back, I should do what??????

I should jump into this forum and explain it. I like when things make sense. You don't need to post in this forum. Send me PM's.

 

[QC]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Eeking out even 1 MPH with some of these combos is a big deal. My boat tested at 62 MPH and I've never seen 58 . . . props, weight balance, trim, load etc. are all important and real data is what makes us all tick. I think that's the point. Let's see if you can find 60+ with the right wheel.

 

[45Auto]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

No issue, sorry if you took it as hostility, probably just a question of semantics. The title of the thread where you posted the initial info (63-65 MPH at 5100 RPM with the 25? prop) was ?What is YOUR boat?s top speed?. I guess I figured that it was your boat you were talking about.

Now you post that your boat will do 60 MPH, but there?s some video of a boat that looks like yours that will go 63-65 MPH by the speedometer. Hopefully it?s at least a GPS speedometer to give you some validity.

Whether is goes 63 with a 25p or 23p, it's a boat/engine/drive with that capability, and there is video proof of it, so I am not getting the issue here.

I just looked at the video you linked in your initial post, and all it shows is some Baja cruising along, no speed or RPM info. Did you mean the video below, which is the same boat but shows the tach and speedo very briefly? Looks like you added a couple of notes below it on Youtube.

http://www.youtube.com/watch?v=gtQ6mRDvNVo

If a couple of MPH are that important to you, use whatever videos you want to justify it. I personally wouldn?t make any claims for the speed of my boat based on a speedometer video of some other boat in some unknown current with an unknown wind. You did notice that he?s going in the same direction of the sailboats he passes?

When someone passes me, I don't care what prop he has (although he might).

Trying to figure out what you mean here, why should anyone care what prop some other boat is using? Prop your boat so it runs where you want it to. Many times even identical boats prefer different props. You?re dealing with manufacturing tolerances. Every hull warps slightly differently when it comes out of the mold. For motors, I don?t know if Mercruiser?s power claims are a minimum, average, or whatever, but I bet there?s easily a 10% range in power output among identical motors. And that?s on brand new stuff, it?s not going to get any better as it gets older. Bottom line is identical boats with identical motors will perform differently.

Then I find the factory spec sheet via Wellcraft: She came with a 23-pitch prop. She did 61 at 4800 RPM as the advertised test speed identically equipped (except for the prop).

If I were taking delivery of a boat and posted it specs, and when it got here it had the wrong prop that held it back, I should do what??????

If spinning a few hundred more RPM and possibly gaining 1 MPH is that important to you, either make whoever delivered it to you meet any specs you agreed upon before you bought it, or start buying props yourself!

Based on the speed for YOUR boat of 60 MPH at 4500 RPM with the 25? prop, 61 MPH at 4800-5000 RPM with a 23" sounds realistic. Your motor should be making over 400 HP anywhere above about 4200 RPM. Propping it to spin to 4800-5000 RPM will let you utilize that last 10 or 15 HP your engine is rated for, which should theoretically (figuring 10HP per MPH) get you about 1-2 MPH in additional speed. That would put you right at the 61 MPH in the Wellcraft specs. Who knows, maybe you?ll see 65 on your speedo. Downside is it will also mean that your motor is spinning about 10% faster at cruising speeds. Kind of like keeping your car out of overdrive while you?re traveling on the interstate. You just have to decide based on how you use your boat.

I should jump into this forum and explain it. I like when things make sense. You don't need to post in this forum. Send me PM's.

Still trying to figure out what you meant by the first couple of sentences here. But I prefer the forums to PM?s, lots more opportunity to learn because of the additional viewpoints/inputs.

 

[H20Rat]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Dude . . . like wow, you didn't need a Welcraft spec sheet to know you were overpropped. Your "Merc" spec for WOT RPM is 4600-5000. No matter what Welcraft or prop calculators tell you this is the ultimate spec period.

There is a HUGE problem with only looking at RPM and assuming the prop is off. Pretty much everyone on here does it, but sometimes you have to dig further into the problem. Knowing what the manufacturer speced the boat to run with is important.

In this case, the guy didn't know if it was the prop that was off, or a tired engine problems. You can't just assume because an engine is lower than its target RPM's that it is the prop. It MIGHT be, but there is a huge list of other conditions that could cause it.

If it WAS the engine, putting a smaller pitch prop on is just a bandaid over a much larger problem, and is not the correct fix.

 

[45Auto]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Eeking out even 1 MPH with some of these combos is a big deal. My boat tested at 62 MPH and I've never seen 58 . . . props, weight balance, trim, load etc. are all important and real data is what makes us all tick. I think that's the point. Let's see if you can find 60+ with the right wheel.

You're right about that QC. Manufacturer spec on my boat is 64-70 MPH, only test I've found on it is a Mercury factory test with the 375HP base motor that showed 61 MPH. Theoretically the extra 50HP of the HO motor should get me about 5 MPH. I've only run it over 60 a couple of times (all the crap starts blowing out of the boat over about 50, wife starts yelling, etc), never really done a WOT run. Maybe if you ever come down to New Orleans we can go out and add a few data points!

 

[QC]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Good points Mr. Crater. I guess my original point was that he didn't need Welcraft data to tell him something was off . . .

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

45Auto has issues that go beyond being helpful in a forum. There is a way to have a discussion, and then there is 45 who chooses some other form of communication.

Hmmm.... at one point, 1MPH matters in this forum, and later -- PRESTO -- it doesn't.

Operating at WOT in the max RPM range is desired, but falling just short of it isn't (or is it)?

Who wouldn't find it interesting to see that the boat rolled off the assembly line with a 23p prop? Jeeze, the prop forum engages all sorts of discussions over a few hundred RPM and a mile or two per hour.

But, since 45Auto has set a tone here, and he has a h-rd on for something related to this subject, we're all over the place.

Thanks all. I was boating successfully for years before getting here and use these forums to expand knowledge a bit and check my sanity. Guess that is frowned upon.

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

There is a HUGE problem with only looking at RPM and assuming the prop is off. Pretty much everyone on here does it, but sometimes you have to dig further into the problem. Knowing what the manufacturer speced the boat to run with is important.

In this case, the guy didn't know if it was the prop that was off, or a tired engine problems. You can't just assume because an engine is lower than its target RPM's that it is the prop. It MIGHT be, but there is a huge list of other conditions that could cause it.

If it WAS the engine, putting a smaller pitch prop on is just a bandaid over a much larger problem, and is not the correct fix.

With a 25p prop she falls short. Wellcraft had her equipped with a 23p from factory and we know the RPM and top speed. Given that information and some other calculations and real world test, one now knows a 23p prop is in order. If I were on a 23p prop as factory stock and dropped to a 21p to regain lost RPM, then lost power might be the case. There'd be trouble to be found. Right now there's been several postings that agree with this premise.

 

[Philster]

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Re: I had a feeling I was overpropped. Now I have the spec sheet and KNOW it.

Good points Mr. Crater. I guess my original point was that he didn't need Welcraft data to tell him something was off . . .

Having Wellcraft data eliminates a huge variable: Engine trouble or other related mechanical problem. As to the "something", that is a wide array of things. The goal is to eliminate variables so that "something" is clearly defined.

 

[45Auto]

Re: I had a feeling I was over-propped...

Re: I had a feeling I was over-propped...

Previous owner claims 70, although he is an absolute idiot who probably used his GPS for the reading while heading out with the current/tide.

Possibly it could pull the 25" prop to 5000 RPM and 70 MPH when newer. Maybe the "idiot" previous owner sold it to you when the engine started crapping out and it couldn't make RPM any more, now the 23" pitch is a band-aid to get it back to recommended WOT RPM. At least it'll be what the manufacturer recommended though.

 

[Philster]

Re: I had a feeling I was over-propped...

Re: I had a feeling I was over-propped...

Possibly it could pull the 25" prop to 5000 RPM and 70 MPH when newer. Maybe the "idiot" previous owner sold it to you when the engine started crapping out and it couldn't make RPM any more, now the 23" pitch is a band-aid to get it back to recommended WOT RPM. At least it'll be what the manufacturer recommended though.

The problem with this speculation is this information -inserted- , which has been referenced several times. It can hit 61 @ 4800 RPM on a 23p prop bone stock (which it is). I can barely get to 60 (and given speedo differences it might be high 50's) on a 25p prop and barely 4400 to 4500 RPM @ WOT.

Now, given everything we know (well you guys know) about props, wouldn't you expect a change from a 23p prop to a 25p prop to drop the RPM by 200-300 RPM and knock top speed down a 2-3 MPH?

All sarcasm aside here. Let's be business-like and focus on the numbers.

 

[jasperpso2]

Re: I had a feeling I was over-propped...

Re: I had a feeling I was over-propped...

Possibly it could pull the 25" prop to 5000 RPM and 70 MPH when newer. Maybe the "idiot" previous owner sold it to you when the engine started crapping out and it couldn't make RPM any more, now the 23" pitch is a band-aid to get it back to recommended WOT RPM. At least it'll be what the manufacturer recommended though.

this isnt out in left field - just sayin...

 

[Philster]

Re: I had a feeling I was over-propped...

Re: I had a feeling I was over-propped...

No, it is out of left field if one has any knowledge of these types of boats. They are not 70 MPH boats with the 502 Magnum.

I operate (at 4400-4500 RPM WOT) a little under the 4600 - 5000 WOT RPM throttle range for the 502 with a light load. I'd like to run closer to 4800-4900 with a light load.

Now, the right thing to do would be to have the engine/mechanicals checked out, which was already done. It's been gone over by a professional surveyor and my marina Merc techs. A compression test was done. I've done all that I am supposed to do, including WOT runs under various conditions. A harsh critic in this thread tells us he never did a WOT run in his very own boat.

If we eliminate mechanical variables, and we say that the only variable left is the prop, and we find it came with a 23p prop and now has a 25p prop, then just about every variable that can be eliminated has been. Bonus: We even know the max WOT RPM and top speed and they all seem to make sense.

So, for the life of me I don't get the confusion here.