JIMBOB Posted June 22, 2004 Report Share Posted June 22, 2004 After my last trip out from christchurch the wake from anouther boat caused me to dip in the shallow water and catch the prop on the bottom Its not to bad and im going to take it to prop revolutions (again!) to sort out but ive noticed that the shaft it sits on is slightley warped, a bit like a buckled wheel on a bike. Ive run the boat after ive seen this and it doesnt cause any shuddering,I think its been like it for a while and the last bash has made it worse I phoned holes bay marine for a quote on repair and they said it would be a new drive shaft and it would cost at least Quote Link to comment Share on other sites More sharing options...
duncan Posted June 22, 2004 Report Share Posted June 22, 2004 Without seeing it it's difficult to comment but one thing that can happen is that you start to lose props - they somehow get shaken undone with bent shafts. This applies to outdrives so I presume it will also apply to outboards. If you can see it then I can't help feeling it's going to stuff some bearings at some point Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 22, 2004 Report Share Posted June 22, 2004 "the wake from another boat caused me to dip in the shallow water and catch the prop on the bottom" ........... surely not !! How long does it take Prop revolutions to repair the prop as my prop is need of some serious repairing. Quote Link to comment Share on other sites More sharing options...
JIMBOB Posted June 22, 2004 Author Report Share Posted June 22, 2004 It happened at 2 riversmeet 10 day turnaround at prop rev at the mo James Quote Link to comment Share on other sites More sharing options...
Afishionado Posted June 22, 2004 Report Share Posted June 22, 2004 After my last trip out from christchurch the wake from anouther boat caused me to dip in the shallow water and catch the prop on the bottom Its not to bad and im going to take it to prop revolutions (again!) to sort out but ive noticed that the shaft it sits on is slightley warped, a bit like a buckled wheel on a bike. Ive run the boat after ive seen this and it doesnt cause any shuddering,I think its been like it for a while and the last bash has made it worse I phoned holes bay marine for a quote on repair and they said it would be a new drive shaft and it would cost at least Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 22, 2004 Report Share Posted June 22, 2004 That'll teach you to go flying through Xchurch harbour at 18knots in 6" of water!! Quote Link to comment Share on other sites More sharing options...
Afishionado Posted June 22, 2004 Report Share Posted June 22, 2004 That'll teach you to go flying through Xchurch harbour at 18knots in 6" of water!! Or for that matter 6 knts in 18 inches of water! Quote Link to comment Share on other sites More sharing options...
Coddy Posted June 23, 2004 Report Share Posted June 23, 2004 Have any of you tried Steel Developments for prop repairs? Web site is http://www.steeldevelopments.co.uk/index.html I have had good reports from a number of people who have used them but I have not had the need yet! Coddy Quote Link to comment Share on other sites More sharing options...
Coddy Posted June 23, 2004 Report Share Posted June 23, 2004 Hi again I have just been reading some interesting stuff about props and cavitation etc. on the Steel Developments site. Reading Jimbobs message I would suggest you get it looked at as soon as possible as the damage you can do is VERY expensive! http://www.propellerworld.co.uk/Steel_Developx.html The above link makes interesting reading if you are into props and how they work Coddy Quote Link to comment Share on other sites More sharing options...
Swainiac Posted June 24, 2004 Report Share Posted June 24, 2004 As a newbie..............can someone explain cavitation please?? Heard Adam use tyhe word last time we were out. Yours bashfully, Rich Quote Link to comment Share on other sites More sharing options...
JIMBOB Posted June 24, 2004 Author Report Share Posted June 24, 2004 cavitation in very basic terms is the prop cutting through air.(im sure someone will expand on this!) James Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 24, 2004 Report Share Posted June 24, 2004 Rich, Read the link in coddies post!..it explains it very well and in great detail. As james says, it is the prop grabbing air. Water has a certain resistance, and therfore the prop can 'grab' against it, when pockets of air, or small air bubbles build around the prop, the blades are effectivly spining in thin air READ THE LINK!! Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 25, 2004 Report Share Posted June 25, 2004 Another good site is Boat Props To summarise : Cavitation Cavitation, (which is often confused with ventilation), is a phenomena of water vaporizing or "boiling" due to the extreme reduction of pressure on the back of the propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can result in physical damage to the propeller's blade surface due to the collapse of microscopic bubbles on the blade. There may be numerous causes of cavitation such as incorrect matching of propeller style to application, incorrect pitch, physical damage to the blade edges, etc... Be advised disturbances in the water flow forward of the 4 propeller can result in blade damage which appears to be blade cavitation, but is actually due to non-favorable water flow into the propeller. Ventilation Ventilation is a situation where surface air or exhaust gasses are drawn into the propeller blades. When this situation occurs, boat speed is lost and engine RPM climbs rapidly. This can result from excessively tight cornering, a motor that is mounted very high on the transom, or by over-trimming the engine. Now what size do I need to Orkney 520 with a 30 HP Honda - Stainless Steel prop Quote Link to comment Share on other sites More sharing options...
shytalk Posted June 25, 2004 Report Share Posted June 25, 2004 didnt know they made stainless props for engines that small i would think the weight of a stainless prop would need half the engines horsepower to get it spinning!!!!!! Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 25, 2004 Report Share Posted June 25, 2004 They do according to the prop web site, however I am having second thoughts about the cost of the propellor compared to the aluminium one and also what the consequences could be if I hit the bottom outside Christchurch with a SS blade rather than Aluminium ( ie. Break Outboard instead of prop maybe ? ) The diameter - pitch on my existing propellor is marked as 9 3/4 X 9 7/8 and the Honda has a gearbox ratio of 2.08 but my engine does not get up to full revs. ( I suspect the bend in one of the blades and the hole in part of the prop has something to do with this ! ). So I am in the market for a new prop and will keep the old one as an "emergency spare" Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 25, 2004 Report Share Posted June 25, 2004 Could this be the reason you go so slow?? Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 25, 2004 Report Share Posted June 25, 2004 I presume you mean weight of prop - ( I haven't actually bought one yet ). I go so slow because the existing prop has chunks out of it - thanks to xchurch - and my boat only has 30 HP+ semi displacement . Still, I don't use as much fuel as some, even with an inefficient bent prop Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 25, 2004 Report Share Posted June 25, 2004 So why does the Sea Angler Orkney 520 get up to 24 knots and cruise at 17??? It only has a 30hp 4stk Mariner/..... Just playing devils advocate????? Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 25, 2004 Report Share Posted June 25, 2004 Strangely, that is a question I keep asking myself !!! What I have worked out is that I need to move weight forward in the boat ( since fitting extra battery ). eg. Just getting Mike to move from the middle of the boat and sit at the front I gain an extra knot !! However, when I bought the boat it ran much better - until I discovered that XChurch has less than 1 ft of water, 3 buoys distance out of the entrance ! (, so it will be interesting to see how it runs once the prop is fixed. I am convinced the propellor is the cause of drop in performance, I can hear the engine is not getting up to max revs, I can see the bend in one of the blades and the hole in edge of another blade can only be bad news !! . My typical speed is 12 knots with a peak of 15 knots if wind and tide are favourable ( as measured by GPS ) Quote Link to comment Share on other sites More sharing options...
Bob F Posted June 26, 2004 Report Share Posted June 26, 2004 Paul, if you are thinking of a SS prop you need to be careful with the size. It is not a 1:1 comparison with an aluminium. If you go to SS it will need to be smaller. Bob F. Quote Link to comment Share on other sites More sharing options...
Coddy Posted June 26, 2004 Report Share Posted June 26, 2004 Hi For Quote Link to comment Share on other sites More sharing options...
Afishionado Posted June 26, 2004 Report Share Posted June 26, 2004 Paul, if you are thinking of a SS prop you need to be careful with the size. It is not a 1:1 comparison with an aluminium. If you go to SS it will need to be smaller. Bob F. Is that so? I wonder why, is it the flexibility factor I wonder? Do you have the reasons Bob? It's just my curiosity and to add to my own knowlege. Mad Mike Quote Link to comment Share on other sites More sharing options...
Paul D Posted June 26, 2004 Report Share Posted June 26, 2004 Bob, Decided to go for a new prop - aluminium one. I bought one from Poole Marine Services along Salterns Way and will be with them by Tuesday. ( Will anyone from the club be able to pick it up for me in the week at all, or I will have to wait until Saturday ? ) Went for Aluminium as the guy behind the counter recommended AL given I will be coming into Christchurch ( I guess a nice strong SS prop will mean instead of a bent blade you risk breaking your gearbox or worst ). I shall then see if I have got the pitch correct - chose the one slightly smaller then my existing prop as the next size was larger and I am not getting to max revs. cheers Paul Quote Link to comment Share on other sites More sharing options...
Afishionado Posted June 26, 2004 Report Share Posted June 26, 2004 Bob, Decided to go for a new prop - aluminium one. I bought one from Poole Marine Services along Salterns Way and will be with them by Tuesday. ( Will anyone from the club be able to pick it up for me in the week at all, or I will have to wait until Saturday ? ) Went for Aluminium as the guy behind the counter recommended AL given I will be coming into Christchurch ( I guess a nice strong SS prop will mean instead of a bent blade you risk breaking your gearbox or worst ). I shall then see if I have got the pitch correct - chose the one slightly smaller then my existing prop as the next size was larger and I am not getting to max revs. cheers Paul I can do it Paul no prob' Mad Mike Ps do you want me to pay for it and then you reemburse me? Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 26, 2004 Report Share Posted June 26, 2004 Will be very interesting to see how it performs!...bet you cant wait?! Quote Link to comment Share on other sites More sharing options...
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