Burned Blade??
 

First here's the specs just fyi:

Formula 353
Mercury Racing 525's
Mercury Racing I.T.S.
Labbed Bravo 32's

After running around this weekend the tip of one blade on the port prop looks like someone cooked it with a torch. I don't think I ever broke 3800 rpm all weekend so it was easy running and I know I never touched the bottom or anything else with it.

Anyone have any ideas what would cause this on only one blade??

Thanks for the help

Re: Burned Blade??
 

Is it possible to supply us with a picture?

Re: Burned Blade??
 

Well now that was pretty stupid of me wasn't it - unfortunately no - boats about 2 hours away and it'll be 2 weeks before I'm back to it.

Re: Burned Blade??
 

What's the condition of the particular blade with the burn (aside from the burn)? Is there anything along the leading edge such as a nick, bend, crack, etc? What about the trailing edge of the burned blade and the blade before before the burned blade? Does the burned blade seem to be bent up or down (when placed on a table)?

Matt

Re: Burned Blade??
 

I haven't gone so far as to take the prop off the boat, but I did give it a good exam and near as I can tell there is absolutley nothing wrong with it or different from anyother blade. No nicks, no signs of cavitation, no bends (that I can see) - nothing. It simply looks like the very tip of the blade (maybe the fisrt inch to inch and half) got hot. It was a real mystery to me so I figured I'd look to those on OSO who know more about it.
Thanks

Re: Burned Blade??
 

When you get the opportunity post a picture. The blade tips travel at the highest speed, about 300 mph, so they are most prone to have issues.

Is the metal discolored as if it was heated? Since you only had problems with one blade the problem probably lies with that blade or the one before it.

Matt

Re: Burned Blade??
 

During the production process at Plant 98, (Mercs propeller facility), a casting may come out of the mold with "fixable" porosity in large sizes, it may be welded prior to balancing and media finish. Depending on its size and the quality of the weld and tech.'s ability, the spot may be evident to the eye after media finish and can show up even better after it is run on a boat. We have had many discussions about this over the years at Mercury. Good arguments from both sides.

Obviously I can't make this judgment call on your prop without seeing it but it is a legitimate possibility due to the explanation you are supplying.

Re: Burned Blade??
 

I'll get a pic when I can, but it'll probably be two weeks. While I've got the pros - if I wanted to change props - what would ya'll recommend given my set up. My first priority would be to improve mid range speed, but like everyone else I want higher top end, higher cruise and better hole shot - not much to ask for right?!?!? I've heard that formula is having good luck with 5 blade props on the 353 because they tend to carry the bow more - any thoughts? Again thanks for the help.
Reed

Re: Burned Blade??
 

Before making a suggestion on props for your application what are your current performance numbers? Is there anything you like or don't like about your current props?

Matt

Re: Burned Blade??
 

I'm just looking for possible performance increases - currently the boat runs right at 50mph at 3500 - 3600 rpm. WOT/5200rpm will get me approx. 84mph, but I'm not a wot kinda guy. Whole shot is a little sluggish, but not a problem. The boat has one funny characteristic in that starting from idle the boat will lumber along until the engines hit roughtly 3000rpm. Once they cross that its like something exloded and they shoot to 4000 plus unless I pull back on the throttles and let everything settle in. I'm not sure I think that's a prop issue, but it's the one thing I'd really like to change if I could.

Re: Burned Blade??
 

Your slip is quite high with the 32 Bravo 1's. Over 18% with 1.5 g.r. You could gain substantially across the board with 5 blade propellers.

We have some 30 Maximus props available if you would like to try them.

We'll wait to see the pictures of the Bravo 1's if you can get some.

Re: Burned Blade??
 

A couple more questions;
Does the boat have a rooster tail when properly trimmed out?
How high do you have to trim to get max top end?
Does the bow seem to be too high, too low?
Even though you may not run your boat at WOT often it's important for the boat to be set up properly and you will find that performance will improve across the rpm range.

Matt

Re: Burned Blade??
 

The boat has the normal Mercury mechanical indicators for drive trim - on those I ususal cruise with the drives trimmed out to only about three on the scale. That equates to just a little positive trim. Set up like that there is no rooster tail at all. At wot my mental picture of the wake is not quite as clear because I'm so focused on what's in front of me, but I would tell you that to get absolute max speed it have to be trimmed very far out - like 7 on the scale and that it does have a little rooster tail running like that. It also takes the boat forever to get up to that speed. It will get to approx 78 quickly, but every mph after that takes a while to build up. I would tell you that the bow seems low and that my understanding is that this is characteristic of 353's.

Re: Burned Blade??
 

I would consider spacers to lower the drives. If you have to trim the drives high to get max top end you probably have a rooster tail.

Based on your numbers from your Bravo 1's a spacer would be in order. 5 blade props may reduce the slip but with the added stern lift the slip may be just as high as it is with the 4 blade props. When slip is as high as yours is I would concentrate on getting the boat running properly before concentrating on your props.

This is assuming that your props are in good repair and they have not been "hacked" on by someone.

The spacers would address most of your concerns. Cruise speed should improve, top end may improve, the bow will be higher, which will allow you to run with less drive trim. The spacers should also address the planning issue you have; the props should not ventilate like they do now at 3000 rpm, also when you get the slip down and run a lower pitch prop the motors won't lug like they do when trying to get on plane.

We will have test spacers available next season so you can try a set of spacers and see how they perform on the boat, just like testing props.

Matt

Re: Burned Blade??
 

Before I say anything else let me freely admit to not being the most techincal person in the world. Spacers will require longer drive shafts - correct? I'm assuming that your reasoning is that the more correct running angle and corresponding increase in efficency will more than over come the increased drag of lower drives?? Given that the boat is still exactly as it came from Formula I'm a little surprised that we would decide that Formula installed the drives to high.

Could ventilation lead to the discoloration on my prop - maybe sucking hot exhaust around the prop or something??

What's your guess at to the dollars to go with spacers and what length do you think is correct?

Again - Thanks
Reed

Re: Burned Blade??
 

Reed,

Boat manufacturers set the drive and due to many reasons they are frequently too high. There is a misconception in the boating industry that the higher the drive the faster you go. This is false.

Drive height is determined by hull design, drive design, power, prop, weight distribution and many other factors. If any one of these is changed it can require a drive height change.

The goal is to have the prop shaft traveling through the water parallel to the direction of water flow. All the thrust from the prop is being used to push the boat forward. Of course no two boats are alike and this can vary a little but as a general rule it works.

A drive spacer kit comes with a flat machined plate that mounts between the upper and lower drive units. It also includes proper length studs and a coupler to transfer the power from the upper vertical shaft to the lower vertical shaft. It's a fairly simple installation which requires draining the drive oil, dropping the lower unit, replacing the studs, put the spacer on the lower and then install the lower to the upper.

Cost of the spacers varies by manufacturer, about $400 to $1100. We will carry a line of spacers and will have spacers available for testing. We don't have pricing on the spacers we will carry yet.

I would start with a 1" spacer and see what the results are and then go from there.

Matt

Re: Burned Blade??
 

Reed

Since the late 1990's manufacturers have continued to raise their drives heights more and more. Fountain, although an awesome boat co., have been a leader in this trend. Heck, even Baja started to do this 3 years ago. Not really a good thing to do with those hulls. The theory is true, less drag you go faster. However, there is a point of diminishing returns and the efficiency actually goes in reverse. With a proper C.G. and a overall light wet weight, plus a boat that carries the bow well, higher "X" dimension's do reap big speed rewards.


Just to clarify, you don't need a longer drive shaft. The kit comes with a coupler that will mate or connect the upper and lower drive shafts.

I would still consider trying 5 blade propellers. Let us know if you're interested.

Spacers can be purchased in 1/2" increments. I believe IMCO has them starting for about $350.



One other thing

Re: Burned Blade??
 

As promised here are pics of the blade in question - any thoughts are greatly appreciated.

Reed

Re: Burned Blade??
 

Last One

Re: Burned Blade??
 

Has the burned blade ever been repaired in the past? Did it ever have a bend in it that was repaired?


Matt

Re: Burned Blade??
 

To my knowledge no. However, the boat was used by the Porter family as their demo for a couple of months - they put about 25 hours on it. I guess they could have done something to it, but that's the only possiblity I know of.

Re: Burned Blade??
 

Well with the history questionable then it is possible that the blade was heated to be re-worked. I don't believe that this has occured from running the boat, it appears to be the result of a repair of some sort. Hope this helps.

Julie

Re: Burned Blade??
 

Wow,

It looks like some one heated the blade to straighten it and never buffed it back out. The fact that it has changed back and forth in color is very strange. I'd like to see a Rockwell hardness test done. Mercury Racing does most all the Fastech props. I can see the code on one of the pictures. We would take raw castings prior to media finish and make them directly to Lab spec. per Thunderbird / Formulas orders. It is possible one group of pourings were bad but that would mean there are others out there too.

I never saw that in 10 years at Mercury other than when a blade was heated with a torch.

?????