Optimize Performance of 90 Merc and Montauk 17

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Author Topic:   Optimize Performance of 90 Merc and Montauk 17

BilgeRat posted 09-25-2010 12:44 PM ET (US)
Mine is a 1998 Mercury 90 2-Cycle on a 1998 Montauk 17. Prop appears to be OEM 21"P Aluminum. At WOT with one person aboard, calm seas, no breeze, 12 gallons of fuel, very little extra gear, GPS indicates about 41MPH, but tach indicates only 5000 RPM. My searches on this site suggest this is the correct prop. Is this performance about right? If top speed is ok, perhaps the tach is faulty. Otherwise, I will need to determine shortcomings of engine performance.
jimh posted 09-26-2010 10:14 AM ET (US)
The estimated maximum speed of a MONTAUK with 90-HP Mercury two-cycle engine is about 44-MPH. Your performance is very close to the estimated maximum, Compare at
http://continuouswave.com/whaler/reference/16-17/repower.html
Tohsgib posted 09-26-2010 11:26 AM ET (US)
Correct prop would be a 20" Laser 2 SS prop, not alum junk. You would fetch the extra 2mph or so.
BilgeRat posted 09-26-2010 09:02 PM ET (US)
Tohsgib/Jimh, 41 MPH is just fine with me as long as engine is running as it should. Most of my use is at moderate speeds in near-shore coastal waters where a lower pitch should give more response to a delicate throttle adjustment when in rough seas, but a lot of use is also in tidal creeks where shallow water, oyster beds, sand bars, etc are the destination. I'm concerned that a high dollar SS prop may not be a prudent use of boat budget in those areas. I am, however, a pretty easy sell when it comes to new boat stuff. If top end performance is not the issue, what is the verdict on prop choice?
jimh posted 09-26-2010 09:31 PM ET (US)
The durability of an aluminum propeller when a blade strike is anticipated is very poor. A stainless steel propeller will have much greater durability. The performance will be better with stainless steel propellers. The cost difference is only about 2.5:1.
Tohsgib posted 09-26-2010 09:41 PM ET (US)
Talk to Tom Clark and get a new Stiletto polished SS prop for "roughly $250". Best bang for your buck.
BilgeRat posted 09-27-2010 07:14 AM ET (US)
Many thanks. I'd like to talk to Tom Clark if he tunes in, or, if we can hook up via e-mail?
Tohsgib posted 09-27-2010 11:49 AM ET (US)
E-mail him.
L H G posted 09-27-2010 07:04 PM ET (US)
If price is an issue, I would get a Quicksilver "Lightspeed" version of a Mercury Laser II prop for that engine. This gives you a high quality Mercury manufactured and designed prop with the only difference in the two versions being absense of the Mercury Performance Vent System on the Quicksilver prop. Quicksilver does not also have the newer intermediate 19" and 21" pitch versions that the Laser II offers.
This guy has excellent pricing and fast service. I have bought two Lightnings from him. They are great performers.
http://www.dansdiscountprops.com/BuyNow/QuicksilverSS.cfm#QuicksilverSS
jimh posted 09-27-2010 08:18 PM ET (US)
Get the propeller from Tom. I never heard of Larry's guy. He is not actively participating here. He probably wouldn't know a Boston Whaler from a Boston Cooler.
Tom will give you better service and better support.
There is nothing about Mercury propellers that brings intrinsic quality. They make them the same way everyone else does--mass production--and they have the same variations inherent in the process.
The last new Quicksilver propeller I bought was terrible. I had to take a file and trim off the flashing from the casting to get it to fit on the propeller shaft. I was not impressed. I sent it back and got a refund.
BilgeRat posted 09-27-2010 09:09 PM ET (US)
I am adamant about supporting those who support me. I've sent an e-mail to Tom Clark and will wait for his reply. I appreciate the value of the experience and expertise he shares on this forum.
L H G posted 09-28-2010 02:36 AM ET (US)
Even though Tom sells Stiletto props, now owned by Yamaha and who makes BRP props for them, I have seen that Tom recommends Mercury Quicksilver props often as an economical alternative. I think he runs Mercury branded props on his own 25 Revenge, and often recommends several of the Mercury models. I use Mercury props exclusively on my Mercury outboards, and think they are the best you can buy. I see Mercury props being used on all brands of outboards quite often, and even by many of the members here also.
But if you really want the lowest cost SS prop, Tom's Stilettos and his excellent pricing are the way to go, and will work on a Mercury.
BilgeRat posted 09-28-2010 07:35 AM ET (US)
Recognizing that any propeller is a compromise on many different features, I am not looking for any particular brand, material, or price...I'm looking for the smartest use of my boat budget dollars given my particular use of my boat. The real value of this forum is that there is a wide scope of indiviuals that have the collective experience to answer my questions without my having to re-invent the "wheel". Many thanks to all.
Dick E posted 09-28-2010 07:23 PM ET (US)
I have the same year, same size & same model of your boat & motor. A twin. My motor is mounted on the top hole.
The standard prop that comes with the motor is an aluminum 13 x 21” pitch it gives good performance.
A stiletto 13 x19” will give you better performance, but the best prop it a mercury Laser 13x 20” prop. A stiletto prop will give you about 2” more pitch than most other manufactures Thus, a 19 “ pitch runs like a 21 “ pitch propeller. The Laser will give you 42-43 mph with 2 people and average load in the boat. It will handle the best of the above propellers.
Tohsgib posted 09-29-2010 12:05 AM ET (US)
Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
Tohsgib posted 09-29-2010 12:05 AM ET (US)
Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
Tohsgib posted 09-29-2010 12:05 AM ET (US)
Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
BilgeRat posted 10-01-2010 02:49 PM ET (US)
It seems that most folks hold the Laser II 13-1/4 X 20 in highest regard for my application. The best price I have found is $390.98 (Merten Marine)including the hub kit and shipping. Is there a better deal to be had?
L H G posted 10-02-2010 01:47 AM ET (US)
For the second time, see my link to Dans Discount Marine above. $279.
Tom W Clark posted 10-02-2010 11:30 AM ET (US)
Doug,
You are generally receiving good advice here. I agree with the propeller recommendations of the 19" Stiletto Advantage, 20" Mercury Laser II or 20" Quicksilver Lightspeed.
All these propellers will give you top performance from your Montauk with its Mercury 90 HP outboard.
To achieve this, you will need to have your motor in the "two holes up" mounting position on the transom.
For the record, let me straighten out some misinformation that Larry has introduced.
The Quicksilver Lightspeed is very similar to the Laser II but not exactly the same. It does not have the Mercury PVS vent holes but instead has the awful large square vent holes that are difficult to plug, and you want to plug them. The blade tips are slightly different as well.
The $279 [actually $294 with delivery] price Larry references above is for the Lightspeed, not the Laser II. Dan's Discount Propellerss does not sell the Laser II. You will have a very difficult time finding a Laser II for less than $400 new.
The Stiletto Advantage 4.25 can be had with hub kit and delivery for as little as $250, an outstanding deal. There is nothing second rate about this propeller.
Stiletto propellers are made by Precision Propeller Industries, Inc. (PPI) which for years made Yamaha's stainless steel propellers. Yamaha was so pleased with their product they bought the entire company a couple years ago.
PPI also makes the Turbo brand of propellers which are more expensive than the Stilettos. They also offer a greater number of propeller models, most high performance.
PPI also makes propellers for Honda and Suzuki. Larry's baseless assertion that they make BRP's props is not true.
I have an account with PPI and have historically helped my Whaler brethren get good deals. I bothers me not at all if another source is used. Dan's Discount Props looks like a very good source based on the pricing; those are grocery store slim margin's they are making based on the prices they publish online.
I have no idea if they are a good business to deal with. I have never known anybody who bought from them but they do sell the Stiletto Advantage 4.25 with hub kit for $274, delivered. That is a very good deal.
BilgeRat posted 10-02-2010 05:27 PM ET (US)
Tom, Thanks for the post. You say to get the most performance I'll need to move motor mounting from one hole up to two holes up. Is "most performance" defined as top speed only? Does two holes up create an increased propensity to cavitate? Mid-range performance is most important to me... for example, in a following sea where boat speed must be judiciously adjusted to the speed of the swells it's best if the engine does not bog down too much when climbing a swell's back, only to have it race ahead on the downhill side.
My engine is turning between 4800 and 5000 rpm at WOT if the tach's indication is accurate. So, I don't want to down size the prop to the point that I may risk over-reving. Is going down to a 19" pitch not going too far?Owner's Manual sez 5000-5500.
Setting price aside for a moment- an aluminum prop can be had for less than $100- and an aluminum propeller is said to be an unwise use of funds. Can it be assumed that the incremental increase in price through the three propellers being questioned represents an incremental increase in performance? I'd rather not spend substantially more that the price of an aluminum propeller unless it is money well spent, but, neither do I want to spend less than enough to get the job done. Good value for the dollar rather than the lowest price is the goal.
Again, many thanks.
face posted 10-02-2010 07:02 PM ET (US)
Bilgerat, Don't go with an aluminum prop. If you hit something in the water, tree limb, bottom, etc and ding the prop, you will have to either have the prop repaired or replaced. An alluminum prop is more likely to be damaged by such a hit. A dinged prop over time will be hard on your lower unit gears because it is out of alignment. The idea that an aluminum prop is more forgiving to your lower unit during a prop strike is the other argument out there, that somehow it is easier on your lower unit gears at time of impact. I think it is very rare that a prop strike, with a stainless prop, actually causes damage to the gears.
Do it right and get a stainless prop!
As for mounting two holes up. No, it is not only about top speed. That being said, propped correctly you will obtain the best top speed. The reason this matters is not because you will race around at an additional 2mph most of the time, rather that this is the best way to "gear" your motor. An over or under propped motor will either lug your motor or over-rev your motor, respectively. This matters throughout the entire range of rpms and directly corresponds to the life of your motor.
To answer your question specifically, yes, generally speaking, raising your motor increases the propensity for a crummy propeller to cavitate in turns and in rough seas. A decent, modern, stainless propeller will not be affected. Lastly it seems you still have 500-700 rpm's left in your upper range to obtain. You will not over-rev by going down 2" in pitch.
face posted 10-02-2010 07:07 PM ET (US)
If you read my current thread about motor height for the Outrage 18, http://continuouswave.com/ubb/Forum4/HTML/007357.html, you will see that going two holes up has made a world of difference for me. I went from a boat that porpoises with the least amount of trim at one hole up to a boat that can be trimmed to my advantage. The overall ride has vastly improved. Get a tube of 5200 3M Sealant and raise the motor, you can always drop it back down. You should gain 200 rpms by raising alone.
-Joe
BilgeRat posted 10-08-2010 11:07 PM ET (US)
So...New Laser II 13-1/4 X 20 arrived yesterday and was put to sea trials today: Gained about 100 rpm to 4900, but lost top speed to about 39 mph. I'm running motor mounted in second hole from the top. Dick E, in an e-mail, says mounting in top hole is best. Tom Clark says to mount two holes up, as does "face" on his Outrage 18 (mine is a Monauk 17). More sea trials to come.
Tohsgib posted 10-09-2010 10:26 AM ET (US)
Something is not right, you should be 43ish.
BilgeRat posted 10-09-2010 01:40 PM ET (US)
I agree. I don't want to overstep the rules of the "Performance" thread, but, I have had the carbs cleaned and new kits installed, de-carbonized the engine, new plugs, drained fuel tank and new non-ethanol gas. Obviously I need to move to the "Repairs" forum and start over. Please look for my thread over there and chime in...I think I need to do something other than move the mounting position of the motor.
Tom W Clark posted 10-12-2010 12:16 PM ET (US)
Tell us more about your boat? Bottom paint? Accessories? Fuel load?
BilgeRat posted 10-13-2010 07:46 PM ET (US)
Tom, Thanks for your interest. The boat is a 1998 Montauk 17. Bottom is in excellent condition- no bottom paint, now or ever. There is an engine mounted trolling motor. At 38MPH and WOT (less than 5000rpm indicated)the boat begins to porpoise with any additional up trim...I did not test the tendency to porpoise with the trolling motor removed...could the additional weight of the trolling motor-maybe 35 lbs or so, sitting aft on the cavitation plate contribute to the porpoise effect? Fuel tank is a 26 gal plastic tank mounted under the RPS. Two batteries are under the center console. All recent tests have been done in calm fresh water with little or no breeze and about 12 gallons or less of 87 grade gas on board. No passengers aboard. Speeds were measured with a Lowrance HDS-7 GPS in two directions. For what it's worth, I re-checked engine compression and all three cylinders indicated 125. The engine is mounted with one empty hole above the top mounting bolt-"one hole up"?
My next test will involve lowering the engine to mount in the top hole (no exposed holes), and then, raise engine to expose two empties on top...and do this with old OEM 13 x 21 Aluminum propeller, and also with new Laser II 13-1/4 X 20 SS. I guess I should remove the trolling motor for these trials, just to eliminate any doubt. What else would you suggest?????
Thanks again, Doug
Tohsgib posted 10-14-2010 11:25 AM ET (US)
Do not lower engine, just raise it, especially if porpoising.
Tom W Clark posted 10-14-2010 12:14 PM ET (US)
Doug -- Engine mounted trolling motor? I suspect the motor it too low, Raise it another set of bolt holes. The last thing you want to do is lower it down.
BilgeRat posted 10-16-2010 04:15 PM ET (US)
Tohsgib/Tom, Thanks for the encouragement. This morning I raised the motor mounting to two holes empty above the top mounting bolt. A quick trip to a local lake proved that performance has definitely improved. RPM's at WOT increased to 5000rpm. The former opposition to steering to port is now gone. I trialed both the original 13X21 Aluminum propeller and the new Laser II 13-1/4 X 20. Can't really say there was much difference, but the OEM had a slight edge on top speed, and the in-gear idle is much smoother and quieter with the lighter aluminum propeller. Top speed is 40 - 41 MPH at 5000rpm. Should I give 3 holes empty a try? I'm willing to let it alone, but there was such an improvement by moving up one hole, moving up two could only be better, right?
Tohsgib posted 10-16-2010 07:11 PM ET (US)
Go all the way up and if you don't like it lower it down.
Fishmore posted 10-23-2010 01:05 PM ET (US)
Bilgerat, I don't want to steal your thread here but would you kindly post an article on your experience with the motor mounted trolling motor. Performance ease of use etc... Thank you.
BilgeRat posted 10-24-2010 09:49 PM ET (US)
I'd be happy to respond via e-mail...I have trouble staying on-topic within the bounds of the topic classifications.

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Author	Topic: Optimize Performance of 90 Merc and Montauk 17
BilgeRat	posted 09-25-2010 12:44 PM ET (US) Mine is a 1998 Mercury 90 2-Cycle on a 1998 Montauk 17. Prop appears to be OEM 21"P Aluminum. At WOT with one person aboard, calm seas, no breeze, 12 gallons of fuel, very little extra gear, GPS indicates about 41MPH, but tach indicates only 5000 RPM. My searches on this site suggest this is the correct prop. Is this performance about right? If top speed is ok, perhaps the tach is faulty. Otherwise, I will need to determine shortcomings of engine performance.
jimh	posted 09-26-2010 10:14 AM ET (US) The estimated maximum speed of a MONTAUK with 90-HP Mercury two-cycle engine is about 44-MPH. Your performance is very close to the estimated maximum, Compare at http://continuouswave.com/whaler/reference/16-17/repower.html
Tohsgib	posted 09-26-2010 11:26 AM ET (US) Correct prop would be a 20" Laser 2 SS prop, not alum junk. You would fetch the extra 2mph or so.
BilgeRat	posted 09-26-2010 09:02 PM ET (US) Tohsgib/Jimh, 41 MPH is just fine with me as long as engine is running as it should. Most of my use is at moderate speeds in near-shore coastal waters where a lower pitch should give more response to a delicate throttle adjustment when in rough seas, but a lot of use is also in tidal creeks where shallow water, oyster beds, sand bars, etc are the destination. I'm concerned that a high dollar SS prop may not be a prudent use of boat budget in those areas. I am, however, a pretty easy sell when it comes to new boat stuff. If top end performance is not the issue, what is the verdict on prop choice?
jimh	posted 09-26-2010 09:31 PM ET (US) The durability of an aluminum propeller when a blade strike is anticipated is very poor. A stainless steel propeller will have much greater durability. The performance will be better with stainless steel propellers. The cost difference is only about 2.5:1.
Tohsgib	posted 09-26-2010 09:41 PM ET (US) Talk to Tom Clark and get a new Stiletto polished SS prop for "roughly $250". Best bang for your buck.
BilgeRat	posted 09-27-2010 07:14 AM ET (US) Many thanks. I'd like to talk to Tom Clark if he tunes in, or, if we can hook up via e-mail?
Tohsgib	posted 09-27-2010 11:49 AM ET (US) E-mail him.
L H G	posted 09-27-2010 07:04 PM ET (US) If price is an issue, I would get a Quicksilver "Lightspeed" version of a Mercury Laser II prop for that engine. This gives you a high quality Mercury manufactured and designed prop with the only difference in the two versions being absense of the Mercury Performance Vent System on the Quicksilver prop. Quicksilver does not also have the newer intermediate 19" and 21" pitch versions that the Laser II offers. This guy has excellent pricing and fast service. I have bought two Lightnings from him. They are great performers. http://www.dansdiscountprops.com/BuyNow/QuicksilverSS.cfm#QuicksilverSS
jimh	posted 09-27-2010 08:18 PM ET (US) Get the propeller from Tom. I never heard of Larry's guy. He is not actively participating here. He probably wouldn't know a Boston Whaler from a Boston Cooler. Tom will give you better service and better support. There is nothing about Mercury propellers that brings intrinsic quality. They make them the same way everyone else does--mass production--and they have the same variations inherent in the process. The last new Quicksilver propeller I bought was terrible. I had to take a file and trim off the flashing from the casting to get it to fit on the propeller shaft. I was not impressed. I sent it back and got a refund.
BilgeRat	posted 09-27-2010 09:09 PM ET (US) I am adamant about supporting those who support me. I've sent an e-mail to Tom Clark and will wait for his reply. I appreciate the value of the experience and expertise he shares on this forum.
L H G	posted 09-28-2010 02:36 AM ET (US) Even though Tom sells Stiletto props, now owned by Yamaha and who makes BRP props for them, I have seen that Tom recommends Mercury Quicksilver props often as an economical alternative. I think he runs Mercury branded props on his own 25 Revenge, and often recommends several of the Mercury models. I use Mercury props exclusively on my Mercury outboards, and think they are the best you can buy. I see Mercury props being used on all brands of outboards quite often, and even by many of the members here also. But if you really want the lowest cost SS prop, Tom's Stilettos and his excellent pricing are the way to go, and will work on a Mercury.
BilgeRat	posted 09-28-2010 07:35 AM ET (US) Recognizing that any propeller is a compromise on many different features, I am not looking for any particular brand, material, or price...I'm looking for the smartest use of my boat budget dollars given my particular use of my boat. The real value of this forum is that there is a wide scope of indiviuals that have the collective experience to answer my questions without my having to re-invent the "wheel". Many thanks to all.
Dick E	posted 09-28-2010 07:23 PM ET (US) I have the same year, same size & same model of your boat & motor. A twin. My motor is mounted on the top hole. The standard prop that comes with the motor is an aluminum 13 x 21” pitch it gives good performance. A stiletto 13 x19” will give you better performance, but the best prop it a mercury Laser 13x 20” prop. A stiletto prop will give you about 2” more pitch than most other manufactures Thus, a 19 “ pitch runs like a 21 “ pitch propeller. The Laser will give you 42-43 mph with 2 people and average load in the boat. It will handle the best of the above propellers.
Tohsgib	posted 09-29-2010 12:05 AM ET (US) Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
Tohsgib	posted 09-29-2010 12:05 AM ET (US) Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
Tohsgib	posted 09-29-2010 12:05 AM ET (US) Ok according to Larry, you MUST buy a US made prop. Hence why I recommend the Stilleto which is made in the USA but we can debate that in another thread since they make props for Suzuki and ??? God forbid you buy anything made from anyone besides Mercury...sorry Tom as I am a sinner.
BilgeRat	posted 10-01-2010 02:49 PM ET (US) It seems that most folks hold the Laser II 13-1/4 X 20 in highest regard for my application. The best price I have found is $390.98 (Merten Marine)including the hub kit and shipping. Is there a better deal to be had?
L H G	posted 10-02-2010 01:47 AM ET (US) For the second time, see my link to Dans Discount Marine above. $279.
Tom W Clark	posted 10-02-2010 11:30 AM ET (US) Doug, You are generally receiving good advice here. I agree with the propeller recommendations of the 19" Stiletto Advantage, 20" Mercury Laser II or 20" Quicksilver Lightspeed. All these propellers will give you top performance from your Montauk with its Mercury 90 HP outboard. To achieve this, you will need to have your motor in the "two holes up" mounting position on the transom. For the record, let me straighten out some misinformation that Larry has introduced. The Quicksilver Lightspeed is very similar to the Laser II but not exactly the same. It does not have the Mercury PVS vent holes but instead has the awful large square vent holes that are difficult to plug, and you want to plug them. The blade tips are slightly different as well. The $279 [actually $294 with delivery] price Larry references above is for the Lightspeed, not the Laser II. Dan's Discount Propellerss does not sell the Laser II. You will have a very difficult time finding a Laser II for less than $400 new. The Stiletto Advantage 4.25 can be had with hub kit and delivery for as little as $250, an outstanding deal. There is nothing second rate about this propeller. Stiletto propellers are made by Precision Propeller Industries, Inc. (PPI) which for years made Yamaha's stainless steel propellers. Yamaha was so pleased with their product they bought the entire company a couple years ago. PPI also makes the Turbo brand of propellers which are more expensive than the Stilettos. They also offer a greater number of propeller models, most high performance. PPI also makes propellers for Honda and Suzuki. Larry's baseless assertion that they make BRP's props is not true. I have an account with PPI and have historically helped my Whaler brethren get good deals. I bothers me not at all if another source is used. Dan's Discount Props looks like a very good source based on the pricing; those are grocery store slim margin's they are making based on the prices they publish online. I have no idea if they are a good business to deal with. I have never known anybody who bought from them but they do sell the Stiletto Advantage 4.25 with hub kit for $274, delivered. That is a very good deal.
BilgeRat	posted 10-02-2010 05:27 PM ET (US) Tom, Thanks for the post. You say to get the most performance I'll need to move motor mounting from one hole up to two holes up. Is "most performance" defined as top speed only? Does two holes up create an increased propensity to cavitate? Mid-range performance is most important to me... for example, in a following sea where boat speed must be judiciously adjusted to the speed of the swells it's best if the engine does not bog down too much when climbing a swell's back, only to have it race ahead on the downhill side. My engine is turning between 4800 and 5000 rpm at WOT if the tach's indication is accurate. So, I don't want to down size the prop to the point that I may risk over-reving. Is going down to a 19" pitch not going too far?Owner's Manual sez 5000-5500. Setting price aside for a moment- an aluminum prop can be had for less than $100- and an aluminum propeller is said to be an unwise use of funds. Can it be assumed that the incremental increase in price through the three propellers being questioned represents an incremental increase in performance? I'd rather not spend substantially more that the price of an aluminum propeller unless it is money well spent, but, neither do I want to spend less than enough to get the job done. Good value for the dollar rather than the lowest price is the goal. Again, many thanks.
face	posted 10-02-2010 07:02 PM ET (US) Bilgerat, Don't go with an aluminum prop. If you hit something in the water, tree limb, bottom, etc and ding the prop, you will have to either have the prop repaired or replaced. An alluminum prop is more likely to be damaged by such a hit. A dinged prop over time will be hard on your lower unit gears because it is out of alignment. The idea that an aluminum prop is more forgiving to your lower unit during a prop strike is the other argument out there, that somehow it is easier on your lower unit gears at time of impact. I think it is very rare that a prop strike, with a stainless prop, actually causes damage to the gears. Do it right and get a stainless prop! As for mounting two holes up. No, it is not only about top speed. That being said, propped correctly you will obtain the best top speed. The reason this matters is not because you will race around at an additional 2mph most of the time, rather that this is the best way to "gear" your motor. An over or under propped motor will either lug your motor or over-rev your motor, respectively. This matters throughout the entire range of rpms and directly corresponds to the life of your motor. To answer your question specifically, yes, generally speaking, raising your motor increases the propensity for a crummy propeller to cavitate in turns and in rough seas. A decent, modern, stainless propeller will not be affected. Lastly it seems you still have 500-700 rpm's left in your upper range to obtain. You will not over-rev by going down 2" in pitch.
face	posted 10-02-2010 07:07 PM ET (US) If you read my current thread about motor height for the Outrage 18, http://continuouswave.com/ubb/Forum4/HTML/007357.html, you will see that going two holes up has made a world of difference for me. I went from a boat that porpoises with the least amount of trim at one hole up to a boat that can be trimmed to my advantage. The overall ride has vastly improved. Get a tube of 5200 3M Sealant and raise the motor, you can always drop it back down. You should gain 200 rpms by raising alone. -Joe
BilgeRat	posted 10-08-2010 11:07 PM ET (US) So...New Laser II 13-1/4 X 20 arrived yesterday and was put to sea trials today: Gained about 100 rpm to 4900, but lost top speed to about 39 mph. I'm running motor mounted in second hole from the top. Dick E, in an e-mail, says mounting in top hole is best. Tom Clark says to mount two holes up, as does "face" on his Outrage 18 (mine is a Monauk 17). More sea trials to come.
Tohsgib	posted 10-09-2010 10:26 AM ET (US) Something is not right, you should be 43ish.
BilgeRat	posted 10-09-2010 01:40 PM ET (US) I agree. I don't want to overstep the rules of the "Performance" thread, but, I have had the carbs cleaned and new kits installed, de-carbonized the engine, new plugs, drained fuel tank and new non-ethanol gas. Obviously I need to move to the "Repairs" forum and start over. Please look for my thread over there and chime in...I think I need to do something other than move the mounting position of the motor.
Tom W Clark	posted 10-12-2010 12:16 PM ET (US) Tell us more about your boat? Bottom paint? Accessories? Fuel load?
BilgeRat	posted 10-13-2010 07:46 PM ET (US) Tom, Thanks for your interest. The boat is a 1998 Montauk 17. Bottom is in excellent condition- no bottom paint, now or ever. There is an engine mounted trolling motor. At 38MPH and WOT (less than 5000rpm indicated)the boat begins to porpoise with any additional up trim...I did not test the tendency to porpoise with the trolling motor removed...could the additional weight of the trolling motor-maybe 35 lbs or so, sitting aft on the cavitation plate contribute to the porpoise effect? Fuel tank is a 26 gal plastic tank mounted under the RPS. Two batteries are under the center console. All recent tests have been done in calm fresh water with little or no breeze and about 12 gallons or less of 87 grade gas on board. No passengers aboard. Speeds were measured with a Lowrance HDS-7 GPS in two directions. For what it's worth, I re-checked engine compression and all three cylinders indicated 125. The engine is mounted with one empty hole above the top mounting bolt-"one hole up"? My next test will involve lowering the engine to mount in the top hole (no exposed holes), and then, raise engine to expose two empties on top...and do this with old OEM 13 x 21 Aluminum propeller, and also with new Laser II 13-1/4 X 20 SS. I guess I should remove the trolling motor for these trials, just to eliminate any doubt. What else would you suggest????? Thanks again, Doug
Tohsgib	posted 10-14-2010 11:25 AM ET (US) Do not lower engine, just raise it, especially if porpoising.
Tom W Clark	posted 10-14-2010 12:14 PM ET (US) Doug -- Engine mounted trolling motor? I suspect the motor it too low, Raise it another set of bolt holes. The last thing you want to do is lower it down.
BilgeRat	posted 10-16-2010 04:15 PM ET (US) Tohsgib/Tom, Thanks for the encouragement. This morning I raised the motor mounting to two holes empty above the top mounting bolt. A quick trip to a local lake proved that performance has definitely improved. RPM's at WOT increased to 5000rpm. The former opposition to steering to port is now gone. I trialed both the original 13X21 Aluminum propeller and the new Laser II 13-1/4 X 20. Can't really say there was much difference, but the OEM had a slight edge on top speed, and the in-gear idle is much smoother and quieter with the lighter aluminum propeller. Top speed is 40 - 41 MPH at 5000rpm. Should I give 3 holes empty a try? I'm willing to let it alone, but there was such an improvement by moving up one hole, moving up two could only be better, right?
Tohsgib	posted 10-16-2010 07:11 PM ET (US) Go all the way up and if you don't like it lower it down.
Fishmore	posted 10-23-2010 01:05 PM ET (US) Bilgerat, I don't want to steal your thread here but would you kindly post an article on your experience with the motor mounted trolling motor. Performance ease of use etc... Thank you.
BilgeRat	posted 10-24-2010 09:49 PM ET (US) I'd be happy to respond via e-mail...I have trouble staying on-topic within the bounds of the topic classifications.