Propellor Erosion

[Rick T]

G'day Fishraiders

has anyone had any experience with their prop eroding due to cavitation? I have a line of erosion on each blade of my prop, my boat has never planed properly but it hasn't bothered me that much that it is worth returning to the store. At this rate I give it another few months and I'll have a hole and have to replace it. Can it be repaired before more damage is done? Will a stainless steel prop fix this prob?

[Grantm]

GDay Rick,

Mate you need to fix the cavitation fault before you fit a stainless prop. Fitting a stainless prop alone wont stop cavitation IMO. How come its cavitating this much?Cavitation to the level where its putting a hole in your prop will ultimately damage the gear box as the prop becomes unbalanced.

Id get it looked at before too much longer just in case. Your Gbox could be quietly sh$%ting itself without you knowing it. Its probably a simple fix.

Cheers :beer:

[basic_fisho]

Good advice Grantm :beer: Ben.

[Rick T]

Thanks Grant, didn't realise it could be doing the gearbox in :thumbsup: I knew the ss prop won't stop cavitation but thought it may not corrode as the aluminium one has ie quick easy fix (although expensive). The bumpy ride has never bothered me, it still gets good pace and I only really notice it on smooth water.

It is the worst cav erosion I have seen, have been thinking of adjusting the height of the motor but not sure if I need to go up or down a hole. she bounces even at full negative trim so it gives u and idea how out of wack it is. Any suggestions who I could take it to check it out around the Penrith area or even better guys that come out, I know if I go back to Hunts they r just going to stuff me around for weeks on end and I don't have the time or patience to deal with them.

[Rick T]

Just spoke to hunts, the porpousing problem is common with hornets (no s@#t sherlock). To be honest I don't think moving the motor height is going to change the way it runs as it has a good top end speed compared to other boats and I don't hear any cav noises, It will probably have to go back to the factory in QLD like Billfish's boat to have work done on the hull. I can't be without a boat that long so if I can fix the errosion prob I will be happy. I'll just put up with the bouncing as I always have and if the prop is ok it won't do any damage to the gbox. They said to take the prop to them and see what they can do. I'll take it down and get on their case to give me a new one. At least I don't have to lug the whole boat down there.

Used to take the Allison to Penrith Marine and they r expensive and I am not confident they will be able to fix the prob anyway.

[Grantm]

Mate id try taking it up a peg or two, sounds like its too low.If the leg is too close to the boat it will force the bow of the boat down.

Bad things happen from this setup, for example poor fuel consumtion. It takes longer to get up on the plane as the motor is working harder. Also because the bow is down it is harder to push through the water, meaning your prop is spinning in dirty water WHICH CAN CAVITATE.

Also check your transom from the inside down the bottom for any cracking (if its a glass boat) alloy should be ok. This can remotely happen on really bad 'bowdown' setups.

Although I said before fix the cav problem before you replace the prop. From your last post I think set up is critical on your boat, therefore you need to start with a new prop in this case fro set up purposes. If the prop is really bad you can get a false reading with trim set.

Before you can set up the boat correctly replace the prop and start from scratch.Take it up a hole ot two first, this will better position the motor in the water (while planing)and take some pressure of the bow.

Hope this helps

[Grantm]

Didnt see your last post about it being a Hornet. Maybe keep a good supply of props on board

[Rick T]

Thanks Grant, great info. I think it is opposite to what u r discribing. I can't keep the bow of the boat down, even on full negative trim. If I trim up at all the bow just bounces continually. Does this mean I should try dropping the motor or have I misunderstood.

Didnt see your last post about it being a Hornet. Maybe keep a good supply of props on board

:ohyeh: Hopefully I can find out if a ss prop will at least not corrode like the alloy is. Its not going to fix the problems but it may save me having to buy a new one every couple of years.

Edited September 27, 2004 by Rick T

[Grantm]

The exact opposite can cause the same problem, but in a different way. Its just about getting the trim right which i believe can be a problem in a hornet, although I have never seen this myself only heard of it.

If the bow is too high the motor needs to come down ( leg sitting closer to the boat ). Definately give this a shot with a new prop.

[Rick T]

Gave the solas fellas a call and u are spot on Grant. They told me try raising the height and maybe a different 12-13 pitch cupped prop. They said s/s will still get cav burn. Anyone had experience in raising the motor height. I presume u use a trolley jack under the skeg to lift the motor and a few fellas to keep it balanced after unbolting?

[Grantm]

Rickt

What ever you do dont put a jack under the skeg of the motor it will snap off for sure.

Undo the motor clamps( hopefully its not bolted on with additional bolts)with TWO people tilt the motor sideways wich will lift one side up. Put a small block(the size you want to lift it ) on top of the transom and under the motor clamp which will lift it up to the desired level. Then do the same on the other side. Be very carefull its a bit tricky. I have done this with motors up to 200hp and its the easiest way. ( Unless youve got an overhaed gantry) Also make sure you undo the steering union so its fully disconnected and maybe the main harness.Dont want any accidental breakages.

If youve got the motor bolted on you now have to make new holes.

Have fun

Edited September 27, 2004 by Grantm

[Robbo]

Rick,

As an alternative to Grant's method.

Under the cowling you'll find a lifting lug/ring as part of the motor. Park your boat under something suitable for hanging a small chain block off. Attach the hook to the motor lug and take up slack so that the chain block is just taking a little weight.

With your Yammie you only need to loosen the 2 bottom bolts and undo and remove the top two. Raise the motor with the chain block one hole setting and then using a suitable aluminium compatable sealant, such as SikaFlex, replace and retension your motor bolts.

Job done.

Although we use motors of the BLACK variety, the job is the same, and this is how we did the motor on my boat and also my mates Top Ender.

I found by rasing the motor on my Hornet to the highest posible setting that I went from using a 13" Alloy Big Blade Prop to using a 13" SS Vengeance Prop. I got simlar top speed, but improved ride characteristics. The Top Ender changed a few props and ended up gaining around 5 to 6 mph top speed.

Give me a yell if you need too.

Thanks,

Robbo

[Rick T]

Thanks fellas, I have a block and tackle that I used on my old hoon cars that I used to build so will be very easy now that I have had a look at it. When I raise it the motor will be in the highest possie like u said robbo. I have a 12 pitch at the moment on the 40 yammie. does changing up to a 13 pitch cupped prop sound about right? The fella at solas sounded like he had done this many a time and was confident doing this would fix the probs. Think I might just order the prop from them and do it right the first time rather than have to slug it out with Hunts. He also mentioned their props are twice as strong and at $150 for allu I'm not complaining.

[Buz]

G'Day Rick,

Do have any photo's of the damaged prop you could put up.

Buz

[Rick T]

I'll take some tonight 4 u guys. Just ordered the new prop, the fellas at Solas are great and sound like they have been through this a few times. Opted for a more expensive alloy prop at $250 but if this one starts to get prop burn they'll give me a full credit towards a s/s prop which they said will be garaunteed against burn damage. Guess my long weekend has just been shortened, will have to move the motor and do some on water testing on the nepean. May have to leave a few bass lures on the boat :ohyeh: . Will post the results next week.

[Guest bluecod]

Rick T,

I changed over to a 50 Yammie on a 4.3 FishRunner and had similar problems trying to get the nose to trim down. I solved the problem by fitting a Hydrofoil to the motor to give it extra lift. Also no "hole" to climb out of when you take off.

Worked for me and something you might consider if the new prop doesn't do the job.

[Rick T]

Had a family member pull out of fishing today so I decided to get back into fixing my cav probs :-mad2 . Pete and I attempted to lift the motor suspending it from the ceiling but the unbalanced motor made it very difficult and we were unsuccessful. Today I did it by myself in 45mins using the boat strap suspended from the ceiling just for safety and to keep the motor upright and put a block under the skeg and lifted the motor height by lifting the tow cup. It made it very easy and no probs with the skeg. After some testing and trying a few props the boat now planes correctly. I can use the trim like a normal boat and no more porpoising. It is now travelling at a healthy 31 knots at 6100rpm. This is 4 knots faster and 400 more rpm. Didn’t hear any cavitation but never could so only time will tell if it fixes that prob. Best thing no foil needed. :thumbsup:

[Grantm]

Good onya Rick, glad to see its all back to normal.