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290 dp aft prop errosion

B

Byron Hunt

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"for Great site , it has been

"for Great site , it has been very helpfull in every aspect

i have a dual prop 290 and im getting serious errosion on my aft prop, it took about five years before it erroded all the way thru the aft prop blade right near the hub (all 3 blades)i had it welded but did not like the results so i purchased a new set fwd and aft prop to the tune of nearly 700.00 for just alum props.i replaced both props thinking that the nicks in the fwd prop were causing the errosion. well i have made about 4 trips since then around 400 miles total and my brand new aft prop is already erroding at the hub really bad and at even faster rate that before. is this nornmal ?? should i got to sst props (800.00 each) or is there some other situation that is causing this. i also have replaced all anodes as well"
 
"Make sure any bonding wires a

"Make sure any bonding wires are in good shape. Just being bolted together doesn't guarantee that the drive won't suffer from electrolysis. The other possibility is cavitation burn, which is more common in bronze or NiBrAl rudders. Contact the prop maker about this."
 
"thanks , could you elaborate

"thanks , could you elaborate on bonding wires ??? this is an unfamilar area for me
also could it be i have a cheaply made or low grade alum prop but im leaning towards your bonding wire senerio since they have erroded
as much in 1/2 year as they did for the past 5 yrs previous"
 
"Byron,
Do you keep your boat

"Byron,
Do you keep your boat in the (fresh/salt) water ? Do your zincs deteriorate abnormally fast too ? If so, then cathodics could be the culprit. When berthed, a neighboring boat may have a shore power cable hanging in the water close to your boat. This can wreak havoc for the boat in question and it's neighbors by creating an unusually large potential difference in the surrounding water, thereby increasing the current flow from the neg anode (your zincs, props and outdrive) to the positive anode (the water around your boat). This could create the unusually rapid deterioration you are experiencing. If you trailer your boat or it's lift kept, then Jim N is correct and your outdrive is most likely improperly bonded. I have a 290 and my transom plate is bonded to the engine via a green wire going from the vicinity of the steering arm to the bellhousing and my stainless trim hoses are bonded to the transom plate via stainless wire braid. Additional bonding is naturally created through your drivetrain and such. I hope this helps to some degree or maybe give you more ideas for troubleshooting purposes.
BZ"
 
"BZ
i live close to the dock

"BZ
i live close to the dock and i trailer the boat in and out each trip.never leave it in the water. i have pulled the engine/bell house several times but the outdrive has never been removed (by me), and i do not recall any wire connected to the bell house or the outdrive at all and i just replaced my trim hoses (which are not sst)and they were not grounded in any way and my zincs after 5 yrs hardly have any errosion. if im not bonded properly wouldn't this effect both the fwd and aft alum props??? the only prop that errodes is the aft prop right up next to the hub on all 3 blades. something has definitly happened since the last engine pull, my aft prop erroded as bad in 1 summer as the old one and its was 5 yrs old. is your 290 a dual prop ??? i will check tonight for some kinda of connecting(bonding wire) and send a close up picture of the aft prop. thanks for all i will be back in touch in the morning
one more thing previous owner install and seawater washdown with the thru hull fitting 2" off the keel to the stbd sides just forward of the transom (just infront of the outdrive)the prop machanic is blaming it on cavitaion from the slightly extruding sea-cock but this dont fly because i have never had this problem and the seawater cock has been there since i owned the boat 7 yrs thanks again"
 
"Grounding is not bonding. Bon

"Grounding is not bonding. Bonding ensures that all of the parts are at equal voltage potential whereas grounding in this case is just using a common conductor in a group of two wire circuits. Technically, grounding shouldn't be used in this application- common is better (or B-).

The bonding wire won't be on the prop but since you mentioned it, you may need a bonding washer. This is just a big star washer, used to bond the prop to the shaft through the propnut. Mercruiser added this due to erosion issues in the past. Call a V-P dealer and see if they stock them. I think this will take care of the problem. If there were parts of a jagged wire that came out from under the propnut when you removed the prop the first time, it may have broken. If it wasn't there, your prop material may be part of the problem. What kind of prop set did you buy and what is the part number?"
 
"Byron,
Have these props be

"Byron,
Have these props been repaired ? Additional thought may be applied to the repair and the material used. Dissimilar materials can cause increased corrosion. The repair material may have dissimilar alloys etc. in contrast to the stock material of your props, thereby facilitating a corrosive atmosphere around them. Just another thing to think about.
BZ"
 
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