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Author Topic:   Montauk 170 cavitation

DLee posted 12-07-2007 10:02 AM ET (US)
I recently picked up a 2003 Montauk 170 with the 90HP Saltwater 2-stroke.
The engine appears to trim down beyond perpendicular with the transom/boat giving what looks like a slight reverse inclination (hope that makes sense...) on the propeller angle.
I had her out the other day in pretty foul weather for a quick launch, run and retrieval. The one opportunitty I had to open her up resulted in what sounded like either cavitation or a spun prop.
The trim was all the way forward so I'm hoping it was cavitation. The condition improved as I trimmed back, but I had also throttled back by this time so the RPM could have corrected a spun prop affect also. I didn't have time or the conditions to open her up again.
My question is: Does the Montauk have a tendency to cavitate WOT with this engine trimmed all the way forward? or do I need to consider a spun prop?
It's getting really cold out here, I'm hoping to get out once more (for longer than a half hour) before I winterize her, any insight would be helpful.
Also, what kind of range can I expect with 12 gallons and moderate speed with this engine? There sure is a lot of talk here about larger tanks.
Thanks, Dennis
GreatBayNH posted 12-07-2007 12:58 PM ET (US)
12 gallons is plenty for a "normal" run on the water. It doesn't leave much wiggle room though if you are on the water running WOT all day. You will want to increase your fule capacity if for no other reason than to give your mind a break. Who wants to be wondering if you have enough fuel all the time, right?
As for caviation. If you have your trim out all the way out(assuming the prop is still in the water) and you punch it, you are going to cavitate. I do it all the time. The key is to make sure you have your engine trimmed properly for the load and watch the amount of gas you are going to give the engine at hole shot.
-Seth
WinniWhaler17 posted 12-07-2007 02:17 PM ET (US)
Another thing you may want to check is the cavitation plate on the motor in relation to the waters surface while under way. I have an '05 with the 90 4 stroke, so slightly different but the principles are the same. I moved my motor up one hole and it made all the difference, if I was going to keep it - it was going up another hole in the spring.
DLee posted 12-07-2007 02:28 PM ET (US)
WW: I think we're on the same page here, but to verify or clarify, the engine does indeed go 'too low' and that can cause cavitation? I don't even know if my engine has a bar for those holes, I'll check. Sounds like you sold your boat?
GBNH: Thanks for the note on fuel, that's kinda the impression I'm getting. As far as the cavitation is concerned -- my curiosity lies in the prop being too low rather than to high. Trimmed all the way down, my prop seems to look as it's actually forward of the transom (sorta).
WinniWhaler17 posted 12-07-2007 03:09 PM ET (US)
Too low or too high can cause it, yes. You want it to be at the optimum height for the greatest efficiency and clean water delivery.
I haven't sold it yet - but it will be gone at some point this winter (sale or trade) as I'm looking to move to the 190MT.
Feejer posted 12-07-2007 03:45 PM ET (US)
Winni
Have you talked numbers on your trade in? I was looking at the Montauk 190, Dauntless 20 and the Outrage 19 at a dealer last Saturday. Its funny how the more you spend on a new boat the higher value amount of your trade in goes.
WinniWhaler17 posted 12-07-2007 03:58 PM ET (US)
LOL! Yeah, it is - isn't it!? Funny, in college I used to work at the dealer that I bought this one from, and will (most likely) buy the 190 from. I have not talked trade in yet, I was going to hit the (big) Boston show in mid. Jan. and see what I could strike for a deal. There might not be a ton better pricing to be had, but there is always that "show perk" that could sweeten the deal.
I was going to start to ask around here what people had paid, or think a fair price to pay is on the 190MT with the 135 Verado. I've seen "list" pricing all over the place - not sure how that happens on a boat with basically the same options but... guess there is a lot to be said for freight, prep and whatever!?
swist posted 12-07-2007 06:56 PM ET (US)
Not to nitpick, but the phenomenon of engine overspeeding due to air (or exhaust gas) being sucked into the propeller is "ventilation", not cavitation. Cavitation happens when the surface pressure of the water against the prop blade is so low that the water actually boils violently, potentially pitting and damaging the prop surface. Cavitation is more likely a result of a prop design problem in conjunction with high water temperatures, and is not directly connected with trim angle.
WinniWhaler17 posted 12-10-2007 11:45 AM ET (US)
swist - good point, I was trying to stay away from that and just keep it basic, but that is very true. There is a diffrerence between ventilation and cavitation - either way, there is a problem and it should be investigated and solved accordingly.
DLee posted 12-10-2007 07:05 PM ET (US)
With any luck I'll get out again this week and the water will be a bit calmer. I suspect the problem is the engine being trimmed too far down. I think that if I can trim the engine so it runs WOT without any trouble, my question of a spun prop will be answered.
Don't you agree?
tmann45 posted 12-10-2007 09:32 PM ET (US)
Does your prop have vent holes and if so, do you have solid plugs or vent plugs?
DLee posted 12-10-2007 10:19 PM ET (US)
tmann, that question left a very dumb look on my face. It's like when my wife speaks Latin to me...
I have no clue. Care to expound? I'll check tomorrow in the light if I know what I'm looking for.
Dennis

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Author	Topic: Montauk 170 cavitation
DLee	posted 12-07-2007 10:02 AM ET (US) I recently picked up a 2003 Montauk 170 with the 90HP Saltwater 2-stroke. The engine appears to trim down beyond perpendicular with the transom/boat giving what looks like a slight reverse inclination (hope that makes sense...) on the propeller angle. I had her out the other day in pretty foul weather for a quick launch, run and retrieval. The one opportunitty I had to open her up resulted in what sounded like either cavitation or a spun prop. The trim was all the way forward so I'm hoping it was cavitation. The condition improved as I trimmed back, but I had also throttled back by this time so the RPM could have corrected a spun prop affect also. I didn't have time or the conditions to open her up again. My question is: Does the Montauk have a tendency to cavitate WOT with this engine trimmed all the way forward? or do I need to consider a spun prop? It's getting really cold out here, I'm hoping to get out once more (for longer than a half hour) before I winterize her, any insight would be helpful. Also, what kind of range can I expect with 12 gallons and moderate speed with this engine? There sure is a lot of talk here about larger tanks. Thanks, Dennis
GreatBayNH	posted 12-07-2007 12:58 PM ET (US) 12 gallons is plenty for a "normal" run on the water. It doesn't leave much wiggle room though if you are on the water running WOT all day. You will want to increase your fule capacity if for no other reason than to give your mind a break. Who wants to be wondering if you have enough fuel all the time, right? As for caviation. If you have your trim out all the way out(assuming the prop is still in the water) and you punch it, you are going to cavitate. I do it all the time. The key is to make sure you have your engine trimmed properly for the load and watch the amount of gas you are going to give the engine at hole shot. -Seth
WinniWhaler17	posted 12-07-2007 02:17 PM ET (US) Another thing you may want to check is the cavitation plate on the motor in relation to the waters surface while under way. I have an '05 with the 90 4 stroke, so slightly different but the principles are the same. I moved my motor up one hole and it made all the difference, if I was going to keep it - it was going up another hole in the spring.
DLee	posted 12-07-2007 02:28 PM ET (US) WW: I think we're on the same page here, but to verify or clarify, the engine does indeed go 'too low' and that can cause cavitation? I don't even know if my engine has a bar for those holes, I'll check. Sounds like you sold your boat? GBNH: Thanks for the note on fuel, that's kinda the impression I'm getting. As far as the cavitation is concerned -- my curiosity lies in the prop being too low rather than to high. Trimmed all the way down, my prop seems to look as it's actually forward of the transom (sorta).
WinniWhaler17	posted 12-07-2007 03:09 PM ET (US) Too low or too high can cause it, yes. You want it to be at the optimum height for the greatest efficiency and clean water delivery. I haven't sold it yet - but it will be gone at some point this winter (sale or trade) as I'm looking to move to the 190MT.
Feejer	posted 12-07-2007 03:45 PM ET (US) Winni Have you talked numbers on your trade in? I was looking at the Montauk 190, Dauntless 20 and the Outrage 19 at a dealer last Saturday. Its funny how the more you spend on a new boat the higher value amount of your trade in goes.
WinniWhaler17	posted 12-07-2007 03:58 PM ET (US) LOL! Yeah, it is - isn't it!? Funny, in college I used to work at the dealer that I bought this one from, and will (most likely) buy the 190 from. I have not talked trade in yet, I was going to hit the (big) Boston show in mid. Jan. and see what I could strike for a deal. There might not be a ton better pricing to be had, but there is always that "show perk" that could sweeten the deal. I was going to start to ask around here what people had paid, or think a fair price to pay is on the 190MT with the 135 Verado. I've seen "list" pricing all over the place - not sure how that happens on a boat with basically the same options but... guess there is a lot to be said for freight, prep and whatever!?
swist	posted 12-07-2007 06:56 PM ET (US) Not to nitpick, but the phenomenon of engine overspeeding due to air (or exhaust gas) being sucked into the propeller is "ventilation", not cavitation. Cavitation happens when the surface pressure of the water against the prop blade is so low that the water actually boils violently, potentially pitting and damaging the prop surface. Cavitation is more likely a result of a prop design problem in conjunction with high water temperatures, and is not directly connected with trim angle.
WinniWhaler17	posted 12-10-2007 11:45 AM ET (US) swist - good point, I was trying to stay away from that and just keep it basic, but that is very true. There is a diffrerence between ventilation and cavitation - either way, there is a problem and it should be investigated and solved accordingly.
DLee	posted 12-10-2007 07:05 PM ET (US) With any luck I'll get out again this week and the water will be a bit calmer. I suspect the problem is the engine being trimmed too far down. I think that if I can trim the engine so it runs WOT without any trouble, my question of a spun prop will be answered. Don't you agree?
tmann45	posted 12-10-2007 09:32 PM ET (US) Does your prop have vent holes and if so, do you have solid plugs or vent plugs?
DLee	posted 12-10-2007 10:19 PM ET (US) tmann, that question left a very dumb look on my face. It's like when my wife speaks Latin to me... I have no clue. Care to expound? I'll check tomorrow in the light if I know what I'm looking for. Dennis