Boat Top Speed

[Musky Plug]

1 hour ago, grimsbylander said:

That 14x17 prop is a good mid range prop for that set up. The issue is, with your numbers you’re running at about 22% prop slip. I’d buy another prop from a dealer that will let you return it if it doesn’t solve the problem. 
What is your hole shot like?? Does it come up on plane quickly?

 

I can’t say for certain how long. Id like to say approx 4 or so seconds. How do you determine prop slip? 
 

[Musky Plug]

I called a couple local places, waiting to hear back from one. Was told I should up the pitch to 19? Would this be a step in the right direction or a waste of time? 

[grimsbylander]

On 9/13/2020 at 2:46 PM, Old Ironmaker said:

 An average 12V battery is closer to 100 lbs than 60 lbs. 

I think this is a bit inflated. Group 31 deep cycle wet cells runs around 70lbs and group 27's slightly less. I do remember the discontinued Sears Platinum was a beast at about 85lbs. I have 4 batteries in my boat and even at +60lbs each I wish I could go to lithium but $$$$$$$$$$$$.

[grimsbylander]

3 hours ago, Musky Plug said:

I called a couple local places, waiting to hear back from one. Was told I should up the pitch to 19? Would this be a step in the right direction or a waste of time? 

What is the recommended WOT rpm for your outboard? You're at 5500 now. For each one change to pitch you can expect a rise or fall in your rpm by around 200 rpm.

I'd look at increasing diameter before changing the pitch since your holeshot seems to be fine. 1/4" diameter change also = 200 rpm

 

Edited September 14, 2020 by grimsbylander

[Musky Plug]

27 minutes ago, grimsbylander said:

I think this is a bit inflated. Group 31 deep cycle wet cells runs around 70lbs and group 27's slightly less. I do remember the discontinued Sears Platinum was a beast at about 85lbs. I have 4 batteries in my boat and even at +60lbs each I wish I could go to lithium but $$$$$$$$$$$$.

 

10 minutes ago, grimsbylander said:

What is the recommended WOT rpm for your outboard? You're at 5500 now. For each one change to pitch you can expect a rise or fall in your rpm by around 200 rpm.

 

Big money for lithium batts. Was talking about this at work today with the sparky.
 

Max rpms are 5500 as per manufacture specs. 

[grimsbylander]

30 minutes ago, Musky Plug said:

 

Big money for lithium batts. Was talking about this at work today with the sparky.
 

Max rpms are 5500 as per manufacture specs. 

OK, then you're right there. Any one change to the prop will cause you to either over or under rev. I'm guessing your gear ratio is ~2.25 on that motor so that puts you at a theoretical 39 mph with no slip(not possible). I'd seriously consider trying a brand new 14x17 so you have a solid baseline you can trust. If the results are the same, I'd increase the diameter 1/4" and see what that does for you. Don't change more than one thing at a time or you'll get lost trying to figure it out.Remember that if you decide to try a 4 blade (increases surface area to reduce slipage), you will need to drop down in pitch by 1-2 inches...start at 1 so 16".

 

[misfish]

On 9/12/2020 at 9:45 AM, aplumma said:

Check the boat for deformities on the back edge called a hook. Remove all excess weight that you have stuffed into the boat over the years. Size and change prop to a stainless steel. Out of all of these your biggest gain will be removing all of the extra crap off the boat that you do not use. Realistically you will not gain 10 mph unless you have a major issue slowing down the boat. For example a Ranger boat with 150 HP GTX (racing series motor) stainless cupped prop with little  to no extra weight is doing 58 mph with a stainless and loses only 3 mph with an aluminum prop. The bottom of a bass boat in this series runs on just a pad when on plane with about a 6 x 4 ft area actually touching the water. your boat will have a much larger wetted surface and will have less improvement on changes. 

 

Art

I had a 18 ft older Ranger, 83 , with a 115 Mariner. Prop was a SS high 5. Hole shot was great . Top speed at 5500 rpm was 56 mph. Speed was confirmed by Terry on a GPS. That was with 2 full tanks of fuel,2 deep cells and a starter. Plus myself and Terry.

[grimsbylander]

26 minutes ago, misfish said:

I had a 18 ft older Ranger, 83 , with a 115 Mariner. Prop was a SS high 5. Hole shot was great . Top speed at 5500 rpm was 56 mph. Speed was confirmed by Terry on a GPS. That was with 2 full tanks of fuel,2 deep cells and a starter. Plus myself and Terry.

That is shocking considering a 115 would be under-powered on an 18' boat. The 320 and 325 Comanche boats were rated for 115hp but were under 16' in length. The 18' 350 Comanche was rated for 175hp. 

[misfish]

6 minutes ago, grimsbylander said:

That is shocking considering a 115 would be under-powered on an 18' boat. The 320 and 325 Comanche boats were rated for 115hp but were under 16' in length. The 18' 350 Comanche was rated for 175hp. 

Maybe it was 17.6. LOL

I no longer have pics as they were on an old PC that crashed, an unable to save. Terry can testify . I had a vid on Photo bucket as well .

[Terry]

Yeah I think it was 17 ft ,but yeah that is what the gps read.  Couldn’t believe it myself but saw it.  

[grimsbylander]

That's FAST.

[Old Ironmaker]

4 hours ago, grimsbylander said:

I think this is a bit inflated. Group 31 deep cycle wet cells runs around 70lbs and group 27's slightly less. I do remember the discontinued Sears Platinum was a beast at about 85lbs. I have 4 batteries in my boat and even at +60lbs each I wish I could go to lithium but $$$$$$$$$$$$.

Batteries today must weigh much more than they did 20 years ago. Because 20 years ago I could carry a battery in each hand with no problem whatsoever. Speaking of Grimsby 30 years ago I came in 2nd the  Peach Festival Men's Bodybuilding Championship. I was the only contestant. 

OK enough hilarity for one evening. I never met a boater that didn't want another 5 miles an hour.  Including an associate in Florida that has a Pete Fountain offshore racer that was complaining he has only hit 100 MPH a few times.  I have politely declined his offer of  a boat ride a few times now.  I don't want to sleep with or feed the fishes.

Edited September 15, 2020 by Old Ironmaker

[misfish]

10 hours ago, Terry said:

Yeah I think it was 17 ft ,but yeah that is what the gps read.  Couldn’t believe it myself but saw it.  

Wish I had pics and the vid. It was a cool ride.

Mark Kulik owned it before me, and Paul at Top Gun maintain it . Maybe he tweaked the engine .

 

It was a 2-4 split, which was nice . You could hear all four fire up when you pinned it.

Edited September 15, 2020 by misfish

[Garnet]

The thing with aluminum props is they flex . And your performance suffers.

It's work to get your boat prop correctly and worth every second. 

[lew]

I've heard it said that a stainless prop doesn't really improve performance over an aluminum prop until your HP is at least 150 but I have no official info on that.

[grimsbylander]

The OP is running at close to 75% of what that boat/motor combination "should" be doing. Switching to stainless on a 90hp will help a tiny bit but in my opinion it's not worth the cost and it's not the root cause. I'd work on solving the 20% then if he's ambitious enough, worry about the last couple mph.  

[grimsbylander]

2 hours ago, misfish said:

Wish I had pics and the vid. It was a cool ride.

Mark Kulik owned it before me, and Paul at Top Gun maintain it . Maybe he tweaked the engine .

 

It was a 2-4 split, which was nice . You could hear all four fire up when you pinned it.

The picture is becoming clearer now lol!!

[John]

I guess being an old guy a few MPH doesn't matter to me. On my Princecraft, 17 1/2', 90 4 stroke, with 2 in the boat and little else we were 39 or 40MPH at WOT, about 5700RPM. Hole shot was pretty good. Was told, by Merc techs that stainless would make little difference on a 90 4ST.

Although my knowledge is somewhat limited I would empty the boat and see where you are. 600# is a lot of weight in a smaller boat. Try the easy stuff first...🙂

[Garnet]

It's the fall off I don't like. Load the boat she just lays in the water.

[AKRISONER]

2 hours ago, lew said:

I've heard it said that a stainless prop doesn't really improve performance over an aluminum prop until your HP is at least 150 but I have no official info on that.

Theres gotta be a lot of factors involved with this, but ive got a 130 horse that does 55mph...that would be a weird outlier though but ya on a 90horse or smaller i dont see how much flex a prop would be getting to change the speed that much.

 

Weight is really the important factor...power to weight ratios are everything, especially the smaller the power you have. Big one being mentioned here is batteries. No need for 3 group 31's in a 16 foot boat.

I fish tournaments with 2 group 27's and a group 24. Run three graphs, livewells and a trolling motor hard this past weekend for 10 straight hours. Not a single issue.

Edited September 15, 2020 by AKRISONER

[Musky Plug]

4 hours ago, lew said:

I've heard it said that a stainless prop doesn't really improve performance over an aluminum prop until your HP is at least 150 but I have no official info on that.

A couple of the places I called also told me this. 

 

3 hours ago, grimsbylander said:

The OP is running at close to 75% of what that boat/motor combination "should" be doing. Switching to stainless on a 90hp will help a tiny bit but in my opinion it's not worth the cost and it's not the root cause. I'd work on solving the 20% then if he's ambitious enough, worry about the last couple mph.  

Maybe the weight is the issue or perhaps the height the motor is mounted at? That’s what I’m starting to lean towards?
 

1 hour ago, AKRISONER said:

Weight is really the important factor...power to weight ratios are everything, especially the smaller the power you have. Big one being mentioned here is batteries. No need for 3 group 31's in a 16 foot boat.

I fish tournaments with 2 group 27's and a group 24. Run three graphs, livewells and a trolling motor hard this past weekend for 10 straight hours. Not a single issue.

I have two group 27 for TM. And 1 group 31 for 3 graphs and everything else. 

Edited September 15, 2020 by Musky Plug

[grimsbylander]

Musky Plug, there's a bunch of info on this thread that will just confuse you because it's unrelated to your issue. 

Verify your tach is correct, verify your prop is good, verify the motor is mounted at a good height for your boat, make sure you're not overloaded (|I don't think you are because you come up on plane well), inspect the hull for any obvious deformities. If all is reasonably good, start tweaking your prop specs. There's a ton of boats like yours out there, ask to meet up with someone to test their prop? Most guys are willing to help! I've borrowed and loaned out my props before. 

[DRIFTER_016]

Do you leave the boat in the water?

Store uncovered outside?

If you leave the boat in the water and water sits in the boat for any length of time the flotation foam can become saturated with water and add hundreds of pounds of weight to the boat.

The only fix for this if it is the problem is to remove the floors and chip out all the wet foam.

Either replace with closed cell sprayfoam or jam a ton of pool noodles in there.

I know one of the big West coast manufacturers has a known issue with this. 

On a 20 foot boat water logged foam can add 600-1,000#'s of extra weight.

[Garnet]

Stainless doesn't improve performance as told by someone that doesn't sell stainless props.

[aplumma]

On 9/14/2020 at 5:44 PM, misfish said:

I had a 18 ft older Ranger, 83 , with a 115 Mariner. Prop was a SS high 5. Hole shot was great . Top speed at 5500 rpm was 56 mph. Speed was confirmed by Terry on a GPS. That was with 2 full tanks of fuel,2 deep cells and a starter. Plus myself and Terry.

I really like the Ranger 350V it is one of the best riding bass boat I have had. I have quite a bit of weight on my pad of the boat with 3 batteries and the 2 fuel cells on board. The rebuilding of the boat with better seats and accessories did add some weight but it is well worth it. I am content to run at 35 MPH all day long because when you floor it you are burning 9/10th of a gallon a minute. I do like the fact that you can usually get ahead of a storm front if it is not moving to fast. 

Art