new prop for the new to me boat

[Hunter65]

I just bought a 2017 Lowe FS1710, it is a aluminum walk thru 17'10" fish and ski boat.
I was wanting to get a spare prop, as I will be mainly on the Mississippi river, fishing, cruising and pulling grand kids on tube.
But then figured instead of a spare why not upgrade

boat Weighs dry 1740lbs
motor 2017 Merc 115hp 4-stroke with 13.25 x 17 Black Maxx prop
with just me , 2 batteries,anchor and 20gallons of gas it runs
5700 at 46mph, comes out of the hole pretty good, not much bow rise

with wife and normal stuff it runs 5300 at 42mph
plan on adding a trolling motor and 2batteries that will go in the bow.

I was looking at the Turning point 13.25 x 17 as a spare, then saw a video on the Merc Spitfire, which is a 4 blade
it says to order the same size as your 3 blade if it performs like it should? Is that true?

If I bought a Spitfire would I order the 13x 17 or 14x 17 ??????

or stay with a 3 blade like the Turning PointHustler

oh, and the motor needs to be raised an inch or so, they bolted it to the top holes in the motor bracket, will do that this week

appreciate any and all input


Dave who likes to catch blue cats

 

[QBhoy]

Hi there. Great to read about others with the same engine.
there is no doubting these engines are throwing out more power than the 115 claimed on the badge. It’s well known by now.
far be it from me to ever doubt you, given I know how good these engines are...but just double check your actual speed with GPs and the rpm too, if you don’t have the smart craft gauges. Far too easy to waste money on props when the info you are working with might not be accurate using dash speedo and tachometer.
I have a CT gearbox version and incredible this engine will push my 19ft deep v cuddy to 43 mph gps on the limiter at about 6100/6150 rpm With a 19” tempest and 44 mph and once or twice 45 mph gps with a 20” enertia at about 6000 rpm at her highest. I’m almost certain you might have the smaller gear case though, given the diameter of that 17” black max you have. I’d stay clear of 4 blades for your gearcase to be honest. Not much use and you have plenty of power on that light boat.
these engines are rated for 5000-6000 rpm and beat near the top of the range in my opinion. The sweet cruising spot is at about 3750-3800 I find.

 

[Hunter65]

I use GPS for Speed tach for rpm
yes I have the smaller gear case,
for an aluminum boat I was surprised on how heavy it is, it performs fine they way it is, saw the Merc Spitfire, advertised better hole shot and keeps the top end speed, so actualy thought I could go with a larger dia, and get more speed then what I have with the same hole shoot

 

[QBhoy]

I use GPS for Speed tach for rpm
yes I have the smaller gear case,
for an aluminum boat I was surprised on how heavy it is, it performs fine they way it is, saw the Merc Spitfire, advertised better hole shot and keeps the top end speed, so actualy thought I could go with a larger dia, and get more speed then what I have with the same hole shoot

All I know of the spitfire is that a friends regal 1900 had a 21” spitfire on it. It did 46 mph gps from memory and bounced off the limiter very easily. As a temporary measure, I put a 19” tempest plus on it...expecting it to hit the limiter just as easy, given the lower pitch. Truth was that the 19” tempest (an outstanding prop I later found out) saw the boat see early 50’s and brought the rpm down by about 100 rpm at 4850 approx. If that helps you judge what the spitfire will be like compared to a really good 3 blade...I hope it helps.
Issue you might have is that there aren’t a great range of props available for that size of gearcase. It sounds like you are doing reallt well as things are to be fair. Naturally you will almost certainly lose top end speed with a spitfire the same pitch as a black max. So have that in mind. I might be tempted by a laser 2 17” if I was you. Will allow a little more trim and lift before it loses grip over the black max...and if it does, might not see any drop in rpm.
As you say, the other factor is if you are going to raise the engine too. Then it’s needing more thought again afterwards perhaps.

 

[Texasmark]

I have a 115 on a similar boat, without 4 fancy, heavy seats, similar hull characteristics and run a SS, 3 blade, Laser II 20P prop getting 47 on a cool day at my rev limiter 5250, boating alone, 20ish gal gas, 3 batteries and gear, sweet spot trim. So I am running your numbers with your 17, wanting to go to 4 blades for whatever reason. I have 3 TP hustlers, 3 of which are 4 blade with the normal TP attributes. One such is cupping on the trailing edge of the blade which few brands of alum. props possess. Other thing is the Hustler is ported and ports give you a faster hole shot (rpms jump up faster) which you indicated was ok now but room for improvement, without affecting WOT performance and improve cruising thrust akin to 4 blade non ported performance.

Running a 14" (which is one of mine, in 3 blades, I bought just to see how it performed on a previous boat) barely fits the lower unit for the 90/115.....14's are made for V6 gear boxes. I had about ¼" clearance between the blade tip and the bottom of the AV plate plus I was already running the "thin" Merc. trim tab and had to notch it for the tip of the blade to clear it, running 19P as I recall...vaguely on another boat/engine.

In short, with what you said, I'd opt for the Hustler, 17P 3 blade in the 13+ inch diameter for my spare.
------------------------
I read the Merc. sales brochure on the 115 regular vs CT lower unit recently as I know they put a 90 hp on the 60 hp CT engine and I was curious as to what made the difference in the 115 engine. The only difference I found in the spec. sheets was that the 115 CT lower unit is running 90 hp gears.....2.33 rather than 2.0:1 that 115s normally run.

That means that the CT can run a higher pitched prop for the same load (in theory) at the same engine rpms and get the same results. I recall back in the 1989 time line when I bought a Ranger with a 115 tower of power (I6) new. The sales brochure for that year indicated that the 90 hp ran the 2.33 gears and was referenced as the "work" related engine whereby the115 was rated as the "pleasure" engine.

I further recall that somewhere I saw a picture of a bulkhead, pile driving barge, having a 90 I6 for propulsion, may have been in that same brochure. I would assume that one would be hard pressed to find a shallow enough pitched prop in the 13+" prop category as it were, for the 2.33, much less finding one for the 2.0 gearbox.....otherwise I see no reason for the difference when we are talking about a gear train and the LU gears and prop pitch are either-or relatives in that calculation.

 

[Hunter65]

Thanks, will order the TP 13.25 x 17 Monday morning

 

[CincyGus]

Not to muddy things and hope the TP works fine for you. But in case it doesn't, I'll share this thread and my situation prior to and after the change to the Spitfire prop I just put on.

https://forums.iboats.com/forum/gen...0615-leave-well-enough-alone-or-make-a-change

Cliff notes version is I increased top RPM when trimmed out by +200, Improved holeshot and acceleration and top end speed. Stayed with the same pitch (14P) and I guess because it is .2" smaller in diameter, that's the reason I increased RPM's.

 

[Hunter65]

Thanks, with me in the boat and fishing gear I hit 6000 rpm, so do not want to go smaller. In fact if I ever figure out the correct way to raise the motor, I may have wanted to go to a higher pitch or diameter.
I have a thread on that now that knows one knows the best way to resolve..
actually they have no idea why I want to raise the motor since the cavitation plate is a couple inches below the boat..

 

[Texasmark]

For normal transom mountings and reasonable speeds, in rough water in particular, having the LU lower in the water helps to keep the prop thrusting, and not aerating...blowing out...ventilating. Only reason you raise it is to "go fast"!

 

[JimS123]

Thanks, with me in the boat and fishing gear I hit 6000 rpm, so do not want to go smaller. In fact if I ever figure out the correct way to raise the motor, I may have wanted to go to a higher pitch or diameter.
I have a thread on that now that knows one knows the best way to resolve..
actually they have no idea why I want to raise the motor since the cavitation plate is a couple inches below the boat..

You don't want to "raise" the motor, per se'. You want to position it where you get the best performance. By "performance" I mean lowest fuel usage and, of course, top speed. "Speed" in itself is of no concern, unless you just want to go faster than everybody else. The faster your capability, the lower the fuel usage at your normal desired speed, and the better your hole shot.

If you want to "change" height, enlist the help of a couple friends. Drop the trailer tongue and lower the engine to vertical. Put a scissors jack under the skeg. Loosen the bottom bolts and remove the top bolts. Change the motor height to where you want it to go and replace the top bolts. Torque all the bolts back down.

If its less than about 60 HP, you don't need the jack. Two guys can manipulate the motor and the third guy can do the bolts.

If you are lucky enough to have an engine hoist, skip the jack and attach the hoist to the ring on the block. If you already have skeg damage, skip the jack as well.

NO boat should have the AV plate below the bottom. At worst, even with the bottom will be OK.

 

[Hunter65]

You don't want to "raise" the motor, per se'. You want to position it where you get the best performance. By "performance" I mean lowest fuel usage and, of course, top speed. "Speed" in itself is of no concern, unless you just want to go faster than everybody else. The faster your capability, the lower the fuel usage at your normal desired speed, and the better your hole shot.

If you want to "change" height, enlist the help of a couple friends. Drop the trailer tongue and lower the engine to vertical. Put a scissors jack under the skeg. Loosen the bottom bolts and remove the top bolts. Change the motor height to where you want it to go and replace the top bolts. Torque all the bolts back down.

If its less than about 60 HP, you don't need the jack. Two guys can manipulate the motor and the third guy can do the bolts.

If you are lucky enough to have an engine hoist, skip the jack and attach the hoist to the ring on the block. If you already have skeg damage, skip the jack as well.

NO boat should have the AV plate below the bottom. At worst, even with the bottom will be OK.

Thanks Jim, you are about the only person who gets it. I have owned boats since 1975, so this is not new to me

You have to remove all 4 bolts, the bottom are not in slots like some motors are.
if you take all 4 bolts out and rest it on the skeg, I would need two guys to hold the 360lb motor vertical, while someone raised the trailer jack and someone shoves the bolt in the correct holes.. plus, per my other post, do you crush the transom cap, or put a spacer where the motor bracket meets the transom?

On other post about the transom, people are asking why raise it, when I state the cavitation plate is 1.5 to 2inch below the hull of the boat

 

[WesNewell]

Only a fool would ask such a question. Most versatile solution would be an adjustable jack plate. Cheapest would be washers or metal plate. You can buy 1 ton hoist for $60 new if you have something to mount it to.

 

[Hunter65]

Only a fool would ask such a question. Most versatile solution would be an adjustable jack plate. Cheapest would be washers or metal plate. You can buy 1 ton hoist for $60 new if you have something to mount it to.

thanks for the name calling, like one lady who was calling the cops name's said, it is just a word.

 

[WesNewell]

I think you misinterpreted what I wrote. i wasn't calling you a fool.

 

[Hunter65]

I think you misinterpreted what I wrote. i wasn't calling you a fool.

yes I did.....

the shop, I would do it myself but due to that cap over the transom , I think I will let the boat shop deal with it. They sell Crestliners which they say has the same cap, and they do one of several things depending on how high they need to go

 

[Texasmark]

NO boat should have the AV plate below the bottom. At worst, even with the bottom will be OK.

Jim sir, you missed this one. Besides my personal experiences , on my current boat to name one, pull up some 1950-60's Outboard sales brochures, OMC I am recalling, and check out where the boat manufacturers and OB manufacturers setup their relationship. Find one that shows the AV at or above a straight edge extension of the bottom.

Besides that, if you have any kind of a keel it plays into your height and performance. My current Crestliner has a significant keel for what it is because that extruded aluminum (keel) is where they weld the side sheets of aluminum in forming the bottom...tongue and groove. I get much better performance under more varied conditions with it slightly below the keel running my SS Mercury Laser II which can grab water if anything can.

 

[JimS123]

Jim sir, you missed this one. Besides my personal experiences , on my current boat to name one, pull up some 1950-60's Outboard sales brochures, OMC I am recalling, and check out where the boat manufacturers and OB manufacturers setup their relationship. Find one that shows the AV at or above a straight edge extension of the bottom.

Besides that, if you have any kind of a keel it plays into your height and performance. My current Crestliner has a significant keel for what it is because that extruded aluminum (keel) is where they weld the side sheets of aluminum in forming the bottom...tongue and groove. I get much better performance under more varied conditions with it slightly below the keel running my SS Mercury Laser II which can grab water if anything can.

As I said in my last post, you want to position the AV plate for best performance. If there is a keel or other variance, then the position is not cast in stone. Modern prop design has changed the whole dynamic as well.

Back in the olden days, motors were relatively low HP and boats were light. We didn't try to "engineer" the rig: we were just out to have fun. When the energy crisis first hit my Engineering Manager gave us the task of reducing energy in every plant process. Making our boats run better was an outgrowth of that time period.

Curious observation.....today I was trolling for the big ones about 50' off shore. Running about 1.5 MPH downstream I happened to pass "Millionaire's Row". One after the other were outboard gofasts with as many as 5 big ones hanging on the back. My observation was that not a single AV plate was below the bottom.

Obviously, most of us don't own million dollar boats, but you get the idea.

 

[Texasmark]

Agree with your comments sir and was aware of the old days and all when I commented....expecting your reply as it was..grin.

When I bought this boat, the PO had the engine jacked up in the highest (4th) hole and was running a 22 pitch Ballistic SS. It didn't do all that well for me when I bought it (dealer was over in E. Tx. about 200 miles and I didn't wait around for a water test as I wanted to make the trip in one day) and in wondering just how that configuration was on a boat that was stumbling at 35 MPH, I spent a lot of time and money on chasing ghosts only to find the root cause as to why....turned out the fuel filter was full of brown !@#$%.

In the process I moved the engine down on the transom where it surely was, coming from the factory, and worked my way up with 3 different props from 17P to the current 20P. I guess he was a member/supporting member of "go-fast sect" and (in retrospect) with clean fuel lines could accomplish his ambitions. Being 79 this week, I now enjoy the softer ride at slower speeds.

 

[QBhoy]

I have a 115 on a similar boat, without 4 fancy, heavy seats, similar hull characteristics and run a SS, 3 blade, Laser II 20P prop getting 47 on a cool day at my rev limiter 5250, boating alone, 20ish gal gas, 3 batteries and gear, sweet spot trim. So I am running your numbers with your 17, wanting to go to 4 blades for whatever reason. I have 3 TP hustlers, 3 of which are 4 blade with the normal TP attributes. One such is cupping on the trailing edge of the blade which few brands of alum. props possess. Other thing is the Hustler is ported and ports give you a faster hole shot (rpms jump up faster) which you indicated was ok now but room for improvement, without affecting WOT performance and improve cruising thrust akin to 4 blade non ported performance.

Running a 14" (which is one of mine, in 3 blades, I bought just to see how it performed on a previous boat) barely fits the lower unit for the 90/115.....14's are made for V6 gear boxes. I had about ¼" clearance between the blade tip and the bottom of the AV plate plus I was already running the "thin" Merc. trim tab and had to notch it for the tip of the blade to clear it, running 19P as I recall...vaguely on another boat/engine.

In short, with what you said, I'd opt for the Hustler, 17P 3 blade in the 13+ inch diameter for my spare.
------------------------
I read the Merc. sales brochure on the 115 regular vs CT lower unit recently as I know they put a 90 hp on the 60 hp CT engine and I was curious as to what made the difference in the 115 engine. The only difference I found in the spec. sheets was that the 115 CT lower unit is running 90 hp gears.....2.33 rather than 2.0:1 that 115s normally run.

That means that the CT can run a higher pitched prop for the same load (in theory) at the same engine rpms and get the same results. I recall back in the 1989 time line when I bought a Ranger with a 115 tower of power (I6) new. The sales brochure for that year indicated that the 90 hp ran the 2.33 gears and was referenced as the "work" related engine whereby the115 was rated as the "pleasure" engine.

I further recall that somewhere I saw a picture of a bulkhead, pile driving barge, having a 90 I6 for propulsion, may have been in that same brochure. I would assume that one would be hard pressed to find a shallow enough pitched prop in the 13+" prop category as it were, for the 2.33, much less finding one for the 2.0 gearbox.....otherwise I see no reason for the difference when we are talking about a gear train and the LU gears and prop pitch are either-or relatives in that calculation.

Not quite accurate there, if I’m fussy.

the 115 ct is very different. Is uses the larger gearcase from the larger engines. You were close with the gearing though. It’s 2.38 ratio.

 

[Texasmark]

Not quite accurate there, if I’m fussy.

the 115 ct is very different. Is uses the larger gearcase from the larger engines. You were close with the gearing though. It’s 2.38 ratio.

Well that makes more sense. I don't remember where I got the info that the gear ratio was the only thing changed....didn't really make sense for a CT conversion.....you want to run a larger prop at lower rpms...gotta have a bigger gear case to make room for the 14-15" diameter.

While we are on the subject of CT, Remember the Scott Atwater 14 hp CT type engine, 1960-70s time line recalling. I forget the gear ratio and size of the prop but that was some LU for a 14 hp Toon Queen.