prop problem

[Glen Hogan]

I keep snapping blades on my 25 Eliminator with twin 300X'S. I've snapped 5 blades on 5 diffrent props 2 were mazco 3 were merc. Anyone have any ideas what's causing this .

[Jay Smith]

Humm,
I'd dial indicated the run out on the shafts maybe bent giving the prop a harmonic problem...

Thats weird...... Breaking them on both engines or just one ?

[Glen Hogan]

Both lowewr units have brand new prop and drive shafts in them. I broke two props before I put new shafts. I thought they were two deep in the water so I've been raising them up more and more . Their about 1.75 above the bottom of the boat directly in front of the lower units. I have 23" of set back so I don't really know how high they need to be. they all broke when I was just cruising around 40-60 MPH, except the last on broke at ABOUT 105 MPH. So I'm just looking for any suggestions THANKS.

[DRHOBACK]

How well does your boat handle 23" of setback as far as planing and porpoising? Did you add the setback, or from Eliminator with that much?
I ask because I have a 24' that has both problems and it has 9.5" of setback.
Danny

[Glen Hogan]

I bought the boat brand new from lightening Bay Marine in florida. They put on 18" Stainless Marine setbacks. Then I rigged the motors and jackplates which are another 5.5". It takes about 5-7 seconds to get on plane and it very really porposis at all . I just don't know how high I should bring the motors up.

[props4u2]

Whenever we have seen this continious problem, the engines were too high causing the blades to thrash in and out of the water excessively. Running hard in choppy to rough water will also cause the same problem.

Lee

[Glen Hogan]

I thought it was because the were to low not to high .What is the rule of thumb for setting the height . Any help would be appreciated.

[150aintenuff]

are they all been lab finished??? if so they may be gettin them to thin to SAFELY hold up to the thrust loads needed to push the boat with out excess flex and rebound as the blade surfaces and then reloads at entry... if they are STOCK out of box then I would say to high.... but 23" back 2 above should be in the ballpark i would think....

just an educated guess...

[Glen Hogan]

They are stock 3-blade cleavers the front of the lower unit is about 36' away from the back of the boat where the step is. The boat runs great until it throws a blade for the heck of it.

[150aintenuff]

ok I stumped... I can understand labbed props throwin blades but stock cleavers??? something is up... your not catching debris unknowinkly are ya?????

[Glen Hogan]

I'm almost positive I haven't hit anything exspecially since it's happened to me twice with Mazco's and three times with Merc's. I thought they were to low in the water which was stressing them out because they were only breaking at 30-5- but the other day I broke the right one at about 105. I still have about 25 lbs. of water pressur at 112. So I thought that ment keep going up.

[150aintenuff]

if your jacks are hydrolic burry them and set your trim at normal running attitude then once ontop and running with the tunnels grabbing air jack up untill speed quits rising or WP falls off.. accelerate another 10-15 mph, do the same over again, peek speed or lose WP eventuially you will be at WOT and jacked as high as props can hold a bite, or gearcases can pickup water... then you will know what you can run elevation wise.... but then moderate your height so that the speed drops JUST slightly due to gearcase or prop drag.. that should be your stopping point and then at the dock mark the Jack or indicator wnd measure on the trailer where your prop CL is I bet your close.... but might be up or down as much as an inch... down would have props las t longer as they remain loaded on bothsides with oncoming and discharging water longer in the swing of rotation. the better equalized the load across all the blades are the longer they are supposed to last...

[props4u2]

Had a customer with a 21' Bullet with a 300x, he would sling blades all the time, all different brands, lowered motor no more blade failure. Yes it did slow the boat down, but not as much as when it slings a blade. We have seen this problem with other boats rigged w/300x's, these are high torque engines wich must be adding to the problem, when you look at the sterndrive boats with big power they either have the props buried or have very thick surfacing props, even they break once in a while.
You can also try not to use excessive trim.

Lee

[150aintenuff]

I thought any trim above neutral +/- 4* was moot with a cleaver.. more trim doesnt help a stern lifter.... or am i wrong on that point....

[mjwalters]

Cleavers still have rake, especially the 32s and 34s. They will lift the bow when you trim.
Glen are your props hanging out into the tunnel?

[Glen Hogan]

My props are way to the outside behind the sponsons. Center to center is about 76'' . I snapped 4 props when the motors were even with the bottom of the boat.when I raised them it seemed to get better i't hadn't snapped one in about 6 weeks and then i't snapped 5 minutes after I took off crusing at about 40 with My girl.

[hsbob]

i know nothing about yor type of boat nor setup. but what happens if you use 4 or 5 blade props. just a question.

[150aintenuff]

what about trying a set of vented bravo 1's, or Maximus??? dont know if they wpould even work but i am sure with vent holes drilled in they might... just throwin out ideas to keep props loaded over more area and not having 1/3 of the prop's surface constantly load and unload which IMO is what is causing the failures of the blades....

[Glen Hogan]

I was tinking of trying 4 blade merc cleavers I just don't know if I should use the same pitch or drop down a size.

[150aintenuff]

if you are righ at the rev limit use the same pitch... will loose 100-200 RPM on average.. if under drop down 1 p and if RPM is high have taht 1 inch bent back in to it at a prop shop..

[Glen Hogan]

Do you think I will loose any speed, will I be able to keep the motors up high .

[150aintenuff]

shouldnt and you should be able to go higher provided wp is still fine... the RPM loss is caused by 1. extra blades drag, 2 higher effeciency-(less slip) 3 pushing more water with more blades( more generated thrust at same slip levels)

when I went to a 4 blade on my boat slip went from 14% down to 8.. unfortunatly speed droped cause I am under powered and couldnt keep engine in its powerband... but if I had the motor to pull the prop I tried I would run a 4 blade on my boat...

[Glen Hogan]

Thanks for the info It's been helpful.