2 inch drive spacer

[dogschool]

I am thinking about adding a drive spacer I've been hearing so much about, can any of my checkmate brethren offer any insight - pros/cons to doing so?
I hear it will add a couple mph - I/O 454mag in an '89 25' Convincor now tops out at 65 on gps - I am also told the spacer will improve hole shot and handling, but thats not a prob now - I am really just looking for inexpensive ways to add hp and a maybe a few mph - any advice appreciated!

 

[vinny p.]

I dont know where you are getting your information but that statement is too vague. Here is how it works. Lowering the bullet by adding a spacer should only be done if you have to. "Have to" can be described as having excessively high slip #'s or some ill handling effects you wish to tame. Simply adding a 2" spacer to a boat that is set up correctly will only SLOW you down. Most of us, myself included are either running or looking to run a shorty lower.

What are your slip #'s?

 

[JW]

Could he be asking about the Land and Sea stern jack? VinnyP is 100% correct, if you add a drive spacer lowering the LU deeper into the water, you'll lose speed unless it's too high and you're getting too much prop slip.

The Land and Sea stern jack will space your outdrive further BACK from the back of the boat, adding leverage and raising your drive height (and adding stress).

 

[dogschool]

Thanks for responding fellas - here is what I am considering: 2" super speedmaster outdrive spacer - I was told about it and found them at cpperformance.com under outdrives and accessories - check it out,
I'd appreciate knowing what you think! try this link for quick access:

www.cpperformance.com/detail.aspx?ID=8207

 

[dogschool]

and wow, vinny, 725 hp in a 25' Convincor? What is the top speed? - that is awesome! I'd like to get 70 mph without spending stupid money to do it - was told this drive spacer alone would gain me a couple mph.

 

[Old Navy]

I put a spacer on and lost speed. (525sc/bravo 1, 283 Convincor) There are enough used ones out there where you can sometimes throw people a couple bucks and "try it before you buy it." 2 inches IS a lot.

 

[vinny p.]

Dogschool,
That spacer is for a #6 drive, which I doubt you have. I know of only 1 Checkmate in the country with a #6. If you really want to try this, you need a Bravo spacer.

http://www.livorsi.com/catalog/bravo.htm

BTW, I depending on conditions and load, I can run 83-85 mph. I found best results by running a -2 shorty lower. Going down with a spacer would kill me.

 

[Old Navy]

I know of only 1 Checkmate in the country with a #6. If you really want to try this, you need a Bravo spacer.



I think that boat does like 114...............HOLY SHXX

 

[dogschool]

Dogschool,
That spacer is for a #6 drive, which I doubt you have. I know of only 1 Checkmate in the country with a #6. If you really want to try this, you need a Bravo spacer.

http://www.livorsi.com/catalog/bravo.htm

BTW, I depending on conditions and load, I can run 83-85 mph. I found best results by running a -2 shorty lower. Going down with a spacer would kill me.

there must be a formula to determine if the specifications of my particular setup would benefit from a drive spacer of a particular size - seems that
they have concluded that moving the outdrive back from half inch up to 3 inches improves performance in one way shape or form - or is that somewhat speculative - or for a particular hull design etc.. Iwould like to know the formula they use. the cost seems reasonable for the claimed gains but obviously the reviews are mixed at best.

 

[vinny p.]

Old Navy,
Not sure how fast it runs, I know its up there. He is from your area.

Dogschool,

The only formula to help determine whether or not a spacer will help os calculating your slip. The formula is as follows:

First you need to calculate your theoretical speed.

((prop pitch X top rpm )/ drive ratio) / 1056 = theoretical speed

then

100 - (theoretical speed / actual gps speed) = slip

If I have confused you, just post your drive ratio, prop pitch, rpm @ wot and gps speed.

 

[dogschool]

vinny, I run a 3 blade ss 23p prop - top rpm 5200 trimmed up- top speed in flat water 63 to 65 mph depending on conditions - in choppy waters I have hit 67 on gps but that is in prestine conditions (low on fuel wind at my back riding solo) not sure what you mean drive ratio - Bravo 1 od - my 454 mag has been beefed up - hi perf heads - roller cam/rockers - hi perf intake/carb
- the prop guys at Delta prop in Cincy told me (based on a similar formula) that my prop was 95% efficient when I considered a 4 balde to gain a little
speed - maybe I need to be satisfied with what I have and with 65 mph in
this boat - though I want to believe there are gains to be had without it
costing a ton, thus my interest in the spacer - btw, thanks for your input!

 

[vinny p.]

Most likely, you have a 1.50 ratio in the drive. I will use that in the equation.

Spinning a 23" prop to 5200 rpm , gives you a theoretical speed of 75.5
Using 64 mph as your top speed, gives you a slip of 15.3 %. Not bad for a 3 blade. I dont know who told you that you are at 95% efficiency or 5% slip. That would be amazing if not impossible.

So, judging by your slip #'s, I would say your prop shaft height is good. The only recommendatioin I would have is to ditch the 3 blade and go with a labbed 26" Bravo 4 blade. That will drop your rpm a bit, but will increase your cruise speed at a given rpm . Save some fuel and wear and tear on the engine as well. Your top speed may go up, but dont expect much.

 

[Lakeside Restorations]

If money is not a huge object you may benefit from going with a 1" shorty & a 4-5 blade prop.. Jamie / lakeside


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[dogschool]

vinny,I tried my friends 26p 4 blade and it dropped my top rpm to 4800 and my top speed to 60-62. I am hoping to get 70mph.

you have mentioned a 2" shorty and now LKSD has mentioned a 1" shorty,
can you elaborate - what is this - are we talking changing the lower unit on my outdrive - at what kind of cost?

based on the stats I've posted, what is a good approach for me to take - money is not a huge object, but spending 5k to gain 2 or 3 mph would be
hard to justify, but spending 3 to 5k to gain 5 to 7 mph would be something
I'd be interested in! I appreciate all the feedback fellas, Thanks!

 

[smallblockford]

not all props are the same some have more bow lift some have transom lift, some slip less they have different propertiees for boats,

vinny p knows what he is talking about his formula is right

makeing a boat fly right is the art you need to learn to run faster without building a moter.

spacers are prob a waste of money, proper prop is big, if you have the moter you are going to run and not change then spend the coin on a labbed prop notice vinny p said labbed.

that meens every blade is right on not a production prop. you will gain 200 to 300 rpm off of a labbed prop that equals one pitch.

i have 1200$ in my prop and having the wrong prop i cant drive my boat past a certain mile an hour because it wants to go over, to much bow lift, air entrapment hulls like transom lift.

 

[smallblockford]

just cause some one is selling something doesnt mean it will do what is claimed, like the guys before said most people want the drive raised.

 

[vinny p.]

As smallblockford said, a box stock prop is not the best way to go.

I may add that getting a " Labbed " prop from someone elses boat may not work well either. I get a laugh when I see labbed props advertised in magazines. The question I have to ask, who the hell was the prop labbed for? You didnt get my information, so the prop isnt labbed for me. If I spend big $$ on a labbed prop, I will be sure that whoever is doing the work, knows what I want and need the prop to do. Better make sure you trust your prop guy as well. I have seen labbed props that ended up being junk.

Now for your #'s with the 26 Bravo prop you borrowed. Believe it or not, that 26" prop is actually a 24.5" For some reason, Bravo 1 props are rated at their maximum pitch, while others , along with the speed formula, use average pitch. There is a 3" pitch progression from the leading edge to the trailing edge in a Bravo prop, thereby giving a 26", an average pitch of 24.5 .
With that in mind, your theoretical speed with the B-1 prop is 74.24 .
You say your saw 60-62 mph, I will use 61 as average. That gives you a slip of 17.6 % . A bit high for a 4 blade. Something doesnt seem right. Maybe the hull didnt like that prop, maybe it is not as advertised.

When testing props, top speed always seems to rate high on the list of priorities. Equally as important is how did the hull feel? Bow high, bow low, blow out on turns, blow out jumping waves, etc..??? Most importantly, did the new prop create any ill handling effects? Mainly chine walk.

Yes, a shorty lower would mean you would have to replace the lower half of the drive. The last I checked, Imco gets about $4500 for a shorty. You can find them used, but they are a hot item. Not easy to find. I searched for about 1 year before I found a good used -2 Imco. Even then, it came with an old style vertical shaft that I had to replace for $500. Luckily, I can tear the drive down myself, so labor is free.

Can you elaborate more on your set up? IE: specific engine specs, do you have good tabs and hydraulic steering? What is the fuel system you are running?

 

[dogschool]

I mistakenly said I borrowed and used a 26p 4 blade, but it was actually
a 24p Bravo 2 which came stock on an '07 27' Convincor w/ 496 ho - that
might help clear the picture - I figure to be around 400 hp considering the
upgrades and certainly not what the 496 is and thats what I blamed for the
drop in rpm and top mph -this boat handles superbly -I have good trim tabs
no hydraulic steering but up and out and on plane very smooth ride, so
no complaints, just want to get the most out of it if more (speed) is possible.
I couldn't believe the right 4 blade prop wouldn't help-now it sounds as if
it might.. what about the prop pitch diff, vinny? Thanks again!

 

[Lakeside Restorations]

Usually the shortened lower is used to reduce drag which usually increases speed.. However sometimes in doing that you will loose some prop bite therefore needing to go with a larger prop or more blades to help keep the bite with reduced drag.. It is an art in doing all of this & one does need to be careful as you can go too high. The good thing is if you are greedy you can go with the 2' shorty and if you went too high on drive height it can be shimmed back down in 1/2" increments to get you where you need to be.. However you cannot go shorter without buying new cases & vertical shafts..

There is usually some speed to be had when going shorter (higher x diimension or drive height)if done right under the right circumstances..

We sell & install the drives, as far as the props Julie @ throttle up props is a good place to get lab finished & custom props.. Jamie / Lakeside

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[vinny p.]

Well, that may explain the excessive slip from the first computation. Here are the #'s with a 24" B-1, remember, actually a 22.5" ..

Spinning a 22.5" to 4800 rpm give you a theoretical speed of 68. Your gps said 61, that puts your slip @ 10.3 % . Which makes more sense. You say it is a Bravo 2 prop. Are you saying it came from a Bravo 2 drive? I have never seen a B-2 on a Checkmate. Is there such a prop called a Bravo 2? If it was in fact a prop from a B-2 drive, how did you get it to fit a B-1 drive? Isnt the diameter way too big?

Again, I agree with Jamie. There usually is speed to be gained from raising the prop shaft. However, it is a juggling act, no science involved. More like trial and error. I also exclusively use Julie @ Throttle-Up for all my prop work.

I think you need to try a good labbed 26" Bravo 1.