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  #1  
Old 06-21-2021, 10:02 AM
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ReelKing ReelKing is offline
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Default 2021 Lowe FS1700 115 Merc & cavitation issue

Hi Guys

I bought a new 2021 Lowe FS1700 115 Merc 4 stroke and love the boat. Comes with four blade 13" prop and I forget the pitch.

The only negative thing I can say is the prop has a cavitation issue. to do a big S turn I need to trim the boat down or I get cavitation issues.

Lowe has the main engine mounted 2nd hole from the bottom. When the engine is trimmed all the way down and I am doing 30 MPH, with the deep V water is shooting out from the side in front of the windshield. If I trim up slightly (not even around 1/4 trim) the water shoots up from behind me but at 41-45 MPH the prop has cavitation issues.

The company I bought the boat from says the engine is mounted correctly. I spoke to Mercury and they said with this boat and engine I should be hitting 51- 52 MPH and not issues. They think the engine needs to be mounted at the lowest setting. I spoke to Lowe and after speaking to them they want to try lowering the engine.

Has anyone had an issue like this, what was the cause, what did you do to correct/fix and what is the outcome?

Thank you

ReelKing
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I-Pilot 80 lb
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  #2  
Old 06-21-2021, 10:14 AM
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Thanks is great feed back, I am lucky and June 29th the dealer has approval from Lowe to cover this under warranty and it will only be in for half a day.

I want to try lowering first and then later look into a new prop. I did learn that when boat sellers order boats they pick the set up including Prop and pitch. Lowe customer support told me in up state NY guys with similar boats and different props are hitting 52 MPH. Same boat, same engine, same engine mount but different prop made a huge difference.

So if lowering the engine mount works, that's perfect, because if I upgrade the prop it should be a win win.
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Lowe FS 1700
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I-Pilot 80 lb
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Old 06-21-2021, 10:16 AM
Hot Runr Guy Hot Runr Guy is online now
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Is it my imagination, or are you actually in the 2nd hole from the TOP?

HRG
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Old 06-21-2021, 10:23 AM
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Quote:
Originally Posted by Hot Runr Guy View Post
Is it my imagination, or are you actually in the 2nd hole from the TOP?

HRG
Good question, it is deceiving. From what everyone tells me Merc has 5 mounting positions (yes there are 5 holes on the mounting plate) and this is mounted 4th from the lowest setting. If we mount this how you suggest the engine will be mounted higher and the problem will get worse
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Lowe FS 1700
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I-Pilot 80 lb
Fish finder - Helix 7 Si G3
Pulled by 2019 Jeep Cherokee Trailhawk
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Old 06-21-2021, 10:31 AM
Hot Runr Guy Hot Runr Guy is online now
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Looks like you have (1) hole left to lower the moter, and (3) available to raise. Lowering the motor should help the cavitation, but probably at the expense of top speed.

You mentioned a 4-blade prop, aluminum or stainless? You're at the point where a SS prop would provide better overall performance. Post a picture of the prop, so we can confirm that they didn't put a 13" diameter prop on a 14" CT (Command Thrust) lower unit.

HRG
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  #6  
Old 06-21-2021, 10:40 AM
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Quote:
Originally Posted by Hot Runr Guy View Post
Looks like you have (1) hole left to lower the moter, and (3) available to raise. Lowering the motor should help the cavitation, but probably at the expense of top speed.

You mentioned a 4-blade prop, aluminum or stainless? You're at the point where a SS prop would provide better overall performance. Post a picture of the prop, so we can confirm that they didn't put a 13" diameter prop on a 14" CT (Command Thrust) lower unit.

HRG
The prop is a 4 blade 13" 17 pitch Mercury Spitfire prop. My engine is four stroke 115 HP (none CT or XS pro model as they weren't an option for 2021, I would have had to wait for 2022 to get this boat with those options)

model 8M8026590
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Lowe FS 1700
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I-Pilot 80 lb
Fish finder - Helix 7 Si G3
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Old 06-21-2021, 11:03 AM
Franco Cialone Franco Cialone is offline
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When I picked up my new boat from the dealer in 2012, a 1625 Lund Rebel XLSS with a 75 Optimax, my motor was mounted just like yours and they installed a 13X19 Black Max. This prop would blow out on turns and gave me about 37-39 mph @5400 WOT, (this is the upper limit of my rev range), I replaced this prop with a 12.9X19 aluminum 4 blade Spitfire and my holeshot improved and no blow-out, revs stayed the same but lost about 1-2 mph. Then I got a 13X17 SS Trophy Plus, my holeshot was instantanious, revs stayed the same but only 36-37 mph @ WOT. So depending on the load of the boat, I will use either the Spitfire or the Trophy Plus, thinking about selling the Trophy Plus and getting a Aluminum 17 P Spitfire, we'll see.
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Old 06-21-2021, 11:09 AM
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Quote:
Originally Posted by Franco Cialone View Post
When I picked up my new boat from the dealer in 2012, a 1625 Lund Rebel XLSS with a 75 Optimax, my motor was mounted just like yours and they installed a 13X19 Black Max. This prop would blow out on turns and gave me about 37-39 mph @5400 WOT, (this is the upper limit of my rev range), I replaced this prop with a 12.9X19 aluminum 4 blade Spitfire and my holeshot improved and no blow-out, revs stayed the same but lost about 1-2 mph. Then I got a 13X17 SS Trophy Plus, my holeshot was instantanious, revs stayed the same but only 36-37 mph @ WOT. So depending on the load of the boat, I will use either the Spitfire or the Trophy Plus, thinking about selling the Trophy Plus and getting a Aluminum 17 P Spitfire, we'll see.
Thanks Franco, my boat has a Spitfire 13" blade with 17 pitch four blade prop. With three guys in the boat, musky gear, full tank of gas, engine slightly trimmed up we hit prop rev limiter around 45 mph We have a video of the cavitation plate above the water and white prop wash causing this. The trim was only SLIGHTLY up. The trim gauge read between the lowest setting and 2nd lowest setting. Simply put this shouldn't be happening which is why lowering the engine should solve this. I can feel the boat and engine want to go faster but simply cant
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Lowe FS 1700
Merc 115 HP
I-Pilot 80 lb
Fish finder - Helix 7 Si G3
Pulled by 2019 Jeep Cherokee Trailhawk
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  #9  
Old 06-21-2021, 12:03 PM
therealjoeblow therealjoeblow is offline
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Not sure about Lowe, but I know for sure with Lund's 2 boats that are very similar to yours, the Impact 1775 and the Adventure 1775, when rigged with the 115 Merc they always put it on the lowest position (top hole on the mounts) when supplying it with either of the the Spitfire 17p aluminum prop or the Spitfire X7 17p stainless prop.

They ony go up higher to the 2nd hole on the 18xx boats with the 150's and higher *and* the 19p Tempest stainless props. Even on the 18xx boats with the stock aluminum props they supply, they still rig the 150's on the lowest (first) hole.

So I'd say almost for certain your motor is too high.

And also, even at the lowest install position, while the Spitfire aluminum is much better than the 3-blade Black Max prop that sometimes gets supplied with the Merc 115, it is not immune to blowout in turns and when trimming too high. You still need to work the trim quite a bit with the Spitfire aluminum.

If you want to nearly eliminate that, you should really consider upgrading to the Spitfire X7. It can handle most turns with a fair bit of trim still engaged, and can trim pretty much to the full usable range without blowout on most boats simply because it is much stiffer than the aluminum version.

Cheers
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  #10  
Old 06-21-2021, 12:13 PM
REW REW is offline
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Reel,
I absolutely would NOT lower the motor.

You are in a pretty good place right now.

It is perfectly normal that if your motor is trimmed up for the best straight line running, that you will have to trim down when making a turn, or when you encounter waves.

I doubt very very much that your boat with its current engine will ever see 50 mph.

On a good day, your boat will see maybe 45 mph - with the prop of your choice and the motor at its best height.

If you go to a 3 blade 19 pitch high rake stainless, you will likely eliminate the cavitation and you might be able to get 46 mph - if you don't cavitate.

But with what you have right now, you are set up perfectly in my mind. Certainly if it were my boat, I absolutely would not drop the motor any lower.

However, I would try two or three different props - and in particular 3 bladed props if you wanted more speed. With todays rigs, it is doubtful that a 4 bladed prop will ever give you as good a top speed as the best 3 bladed prop will do for your rig.

Right now, you have a pretty good all around rig. I would likely leave everything alone, unless I wanted to try some different props.

You might try 3 bladed stainless props in 15 pitch, 16 pitch, 17 pitch, 18 pitch, 19 pitch, 20 pitch and 21 pitch.

If you do, I expect that you will get your very best overall performance with a high rake 18 pitch prop - with the motor adjusted to do its very best - which might be right where it is at right now, or up or down some.

-------------------------------
By the way, if you have your boat on the trailer and if you adjust the trim on the motor so that the motor is exactly vertical - run a straight edge out from under the hull so that you are extending the bottom of the hull by use of the straight edge, measure the positive distance from the underside of the motor cavitation plate to the top of the straight edge which is essentially the bottom surface of the hull.

Normally, when a boat and motor are working really well together and the prop is of a design to really grab water that the motor height will be such, that the underside of the cavitation plate will be two inches ABOVE the bottom of the hull.

Normally, if the cavitation plate is flush or lower than the bottom of the hull, you will have a more stable boat, but at the expense of performance.

Could you perform that measurement on your rig? i.e. have the lower unit of the motor parallel with the face of the transom. Then, extend the bottom of the hull by virtue of a straight edge held tight to the underside of the hull and then measure the positive or negative distance from the underside of the motor's cavitation plate to the top side of the straight edge.

i.e. what is the distance of the underside of the motors cavitation plate with respect to the bottom of the boat's hull?


Thanks for any updates.

p.s.
If You want your boat to be a 50 - 55 mph boat, remove your current motor and replace it with a 150 hp motor. I realize that the hull may not be rated for that motor, but if you want the 50 mph speed - add another 35 hp to your current engine and you will achieve that speed.
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