What could I expect the speed difference to be using identical pitch,rake and diameter props. The only differerence being different Mercury HP ratings. Example 850 HP props vs. 1200 HP props. Another would be 850 HP vs. 1500 HP. What top end Mph could I expect to lose due to the thicker blades? Thanks Doug

Good question

Brett @ BBlades. Anything. I know the thinner blades should have less drag. Any real life numbers.

Nce thread, and looking forward to hearing some results from experience.
I would assume that faster you boat is to start with the bigger the difference is going to be.

Thin to win Baby! (and thin to break and leave you stranded)

I am not going to write a book here. Although, the potential is overwhelmingly present and the data and history abundant.

The differences in speed/performance can be somewhat small and other times can be quite staggering. When you are talking about the thicknesses you are mentioning the gains will be substantial.

There has been an awful lot of discussion, engineering and testing revolving around this subject. I have been fortunate to be part of it my entire career at Mercury, Mercury Racing, and BBLADES. It is something that we constantly investigate. We have developed many "thickness curves" over the years for just about every propeller Mercury, Hering, Hydromotive and others produce. The term thickness curve is not a BBLADES term but rather a description invented at Merc Racing many moons ago. This is term only used by Mercury and BBLADES as far as I am aware. Now others may have picked it up just as many have picked up other terms invented at Mercury Racing. One continually repeated that come to mind is "lab Finishing" LOL Dennis Cavanaugh and Bob Hetzel drew up the original thickness curves on a few cleavers in the1980's and we have been modifying them since.

In order to not divulge any of BBLADES trade secrets, I will only tell you the obvious and that is a thickness curve is just as stated, the thickness of the blades. Of course it goes much deeper than that but for this question that answer suffices. One thing I can tell you is we take the blade thicknesses seriously. By that I mean, we don't just thin the blades, we thin them to specific specs in specific areas. There is science here with a bunch of background.

Ok, there are many variable that affect what the actual gains will be from thinning blades. The boats design is a start, HP and torque curves, current efficiency (slip %), size of the thickness adjustment etc. etc. As a starting example we can look at Lab Finishing a typical Mercury Bravo 1 or Hydromotive Quad 4. These propellers will typically see a 1-4 mph increase in speed due to the thinning process. So we can take 2-3 as a average. When looking at #6 style cleaver propellers let's conider a 1500hp prop as box stock. A 1200hp prop would be a standard Lab Finish for the 1500hp prop and a potential 2-3 mph gain could be had. Going to the next level of thinning at 900hp thicknesses could reap another 2-3 mph and ultimately the 600hp level could give you a total of 6-10 mph. (if the blades didn't fall off).

These are rough examples but I feel are appropriate in explaining the gains. This is not to say you will see 10 mph on the top buy unbolting your 1500hp props and bolting on 600hp props. But there will be gains and they will be pretty big.

A example I liked to use often a few years ago when we did many 3bl OB cleavers a season was basically the same numbers as above. On a 28-32 foot Skater or Doug Wright with twin 280's we could see a 4mph gain Labbing stock propellers. Going to the our race thickness curve would get us another 3 mph (give or take). If we went to the kilo thicknesses we could see another 2-4 mph but the blades were getting to a point of a short life span. Again, the progression of these thicknesses are key to performance and longevity.

One question that always comes up is, if you Lab my propellers, are they going to break? One of the things we did while engineering the thicknesses of the blades was to take that question into consideration. Standard Lab thicknesses on props such as Bravo 1's, Maximus's, p5X's, Q4's etc. are capable of running under normal conditions without failure in application of 900-1000 hp. (although not originally intended to) Failures are usually due to dings and dents that are not maintained, under water strikes or, unfortunately, casting flaws within the casting. Casting flaws are reality. They are a nightmare for us at BBLADES. While I am mentioning castings. All propellers built by the major manufacturers in the US are castings, NOT forgings. Except the Hering #6 style forgings specific. So, CNC'd propellers from Mercury or Hering are castings. Mercury offers thicker (slower) propellers for big HP and Hering offers forgings (expensive) for higher HP. A thicker casting or a Forginging can fail as well. During the recent record setting V bottom record setting event, more than one set of props broke. Just because a propeller is CNC'd doesn't mean it is a forging. Also, just because it is CNC'd doesn't mean it is perfect because, guess what, none of them are perfect. Ok, I digress.

I hope this sheads some light on the subject. Like a stated at the beginning, there is a lot to thicknesses and we have devoted that much time to perfecting the art.

Brett

Thanks Brett. I will be sending a set of speedmaster props to you, taking advantage of your free shipping offer. Doug

Well I learned something today!