Prop Discussion

[Ytmsn]

I'm about to pull my props and have them serviced before the season hits. I nicked one at the end of the season last year and got a thumbnail sized ding in it but bent it back with a crescent. So I'm taking them in.

My buddy at the Boat City Prop Shop in OKC is a prop guru and has been in the business for over 30 years. I pretty much just do what he says. If he knows you he'll let you take 2 or 3 different props for testing to get to see what you like, but I'm just interested in getting mine back to perfect.

I already know what I'm going to do, but I thought for the sake of discussion and for the benefit of some of our newer members we could talk about satin versus polishing. Labbing/Lapping (depending on what you type into the search bar) What clocking means, what Cupping means, what it does, etc..

I learned most of what I know from reading the Enquirer and on the innerweb....

Matt?

[NautiGirl]

I will need Matt to post a response pre-lemonade and then post-lemonade.

Between him and BBP we should have this topic covered.

[cmattj]

I already know what I'm going to do, but I thought for the sake of discussion and for the benefit of some of our newer members we could talk about satin versus polishing. Labbing/Lapping (depending on what you type into the search bar) What clocking means, what Cupping means, what it does, etc..

I learned most of what I know from reading the Enquirer and on the innerweb....

Matt?

No worries just Coffee.

Duo prop out-drives are purpose built for efficiency. (Merc or Volvo) they are designed for reducing slipping in propulsion at steady speeds. This is Not pertaining to Volvos DPX Duo prop performance drives, or Mercury Black Hawk duo semi surface piercing drives) as those are a shallow depth set ups with high X - dimensions (out-drive location in relation to bottom of the boat) to leave as little of the out-drive in the water as possible. Less Drag equals speed!!

Prop Pitch is calculated a ZERO slippage for example a 26 Pitch prop is calculated to move 26 Inches in one rotation. So now lets chat!
Your limited on the low hanging large 6 blade set ups as they are great for taking off and holding cruise speed with limited slip, but they are awful at overcoming higher speed drag. So lets not overthink duo props trickery in obtain performance as they fight themselves just in the design as what they are intended to do.

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2019-02-13 08_00_54props.jpg

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Race boats use 4 blades.... 5 blade and in a Cleaver style to keep them slipping and accelerating at the same time. So when prop shops talk about tricking out Volvo F series props and or Mercs Bravo 3 props.. Take a breathe.....You must keep it simple and go for Balance and Blade rake equality. Thats about all you can do unless you try companies different theory on Bow or Stern lift as they design in the angel of rake built into each blade.

Labbing

Reducing the exiting resistance of a Prop blade to help it free up and obtain a higher pitch number along with a higher rpm. It usually includes thinning the edge blade (razor sharp) and creating a low resistance prop.

A boat that struggles to hit the rev limiter with a prop can benefit from this but now the prop is fragile for nicks and general abuse.

Satin Vs Polishing

Satin is the most common after a prop shop will change rake or repair bent blades. They also trim edges and tips that have chips and gouges so this method hides a lot of the repair work, and gives the prop and nice look over all. Some props thin the last bit of the edges with a satin 1/4 inch tail as this thin tips and inside no burrs. Its looks cool as well !!
Polishing is thought to allow the resistance of friction to be reduced but is time and labor extension on a repaired prop.

Cupping

"I put some cup in it " the prop guy said...

Take that same edge of the Blade we just discussed in Labbing, and give it a slight forward lean to create increased blade traction and reduce slipping.

More common on a 3 and 4 four blade single out-drive props, as they tend to hold the high slip percentage, and as a benefit of achieving a better cruise speed. Not designed to gain higher rpm or to increase MPH.

Clocking

The 6 blades ( 2 X 3 = 6 ) you have on these wonderful in effective duo props have been theorized to create such a turbulence in full throttle operation that cavitation and resistance to forward propulsion is felt to happen .

Since the props are counter rotating, the props may cross paths at the same time under the Cavitation plate of the lower unit. By clocking the props to avoid this occurrence is can reduce the turbulence and cavitation... so you can achieve a higher rpm along with forward propulsion when accelerating. Top speed improvement.

So in closing .. Keep it simple .. Keep them balanced and clean and don't over think whats Volvo and Merc have already designed for your Hull design, and all-around best handling and performance.

Prop shops are there to repair props more than they are to improve them. Companies like "B Blades" and other study rake angle and design as they can Taylor a need for your specific goal and most likely achieve it.

[NautiGirl]

Well I caught about 2/3 of that. Matt I feel like we should discuss this over a bourbon and lemonade a the next meet up. I am more a visual person, and surly the drinks will help the discussion.

[liquid]

Do me, do me next!

[Spine Guy]

Well I caught about 2/3 of that. Matt I feel like we should discuss this over a bourbon and lemonade a the next meet up. I am more a visual person, and surly the drinks will help the discussion.

HAHAHAHA!!! I was in over my head right away.

[AsLan7]

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Great post regarding the science of propellers and thrust Matt.
Informative, factual, and with pictures no less! Well done my Donzi friend!

Btw, one other option is to switch the forward and reverse gearing within the outdrive like Reggie Fountain did in the 24CS allowing him to pick up 1 more mph using the same reverse pitched prop. Who knew!
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[MnLakeBum]

Yes, great post, thanks!! I unfortunately dinged both of my Volvo props last summer and now have an extra set of props and my son and I have first hand knowledge of how to remove and install the new forward drive props while standing in chest deep water under the boat lift!! My rebuilt props did give me the exact same top end as before the damage so I believe I have my local propeller shop.

[Jeeper]

Does anyone know a good place to buy a set of spare props for a R5 Surf? The dealer quoted me $1800 I thought that was a little steep.

[Big Block Power]

Does anyone know a good place to buy a set of spare props for a R5 Surf? The dealer quoted me $1800 I thought that was a little steep.

Call bblades.
Great post Matt. I was lost at the 1st paragraph of Yt.

[Big Block Power]

I'll post a good before and after pictures of a few examples of what Matt is taking about when I get them back.

[MnLakeBum]

Does anyone know a good place to buy a set of spare props for a R5 Surf? The dealer quoted me $1800 I thought that was a little steep.

I paid $1,640 plus tax for the props from my dealer last July but at the time I didn’t want to deal with shopping around especially since they treated me right on the price of the boat and two hydraulic boat lifts they sold me.

[Ytmsn]

Matt you're the bomb. I knew I could count on you!

[akorcovelos]

In regards to clocking the dual props, according to Mercury that is only required on the Blackhawk performance dual prop drives. Bravo 3 does not require clocking per the service manual. That said, I still clock mine, can't hurt, right?

BBlades and lots of bleeding edge performance boaters say the satin finish is faster than polished, but at the cost of longevity due to accelerated corrosion in salt, and adding stress risers across the blade faces. For this discussion on a Cobalt forum, the difference is nominal, and polished looks cooler, lol.

[TXsurfer]

Yes, great post, thanks!! I unfortunately dinged both of my Volvo props last summer and now have an extra set of props and my son and I have first hand knowledge of how to remove and install the new forward drive props while standing in chest deep water under the boat lift!! My rebuilt props did give me the exact same top end as before the damage so I believe I have my local propeller shop.

Curious if you needed any extra tools? Special socket or something? I’m about to find out how much fun this is sadly after bending one of the front prop blades almost in half. Stumps!!

Appreciate any tips and tricks!