Mercury 20hp only getting 21mph normal?

[jlrosine]

Hi all, I have some questions and hopefully I'll get some suggestions on what to do next.

Problem (or so I think). I can only peak at about 21mph, and getting on plane takes a long time (struggles without weight in front). I have a 14' Tracker V Guide boat, no console so it's pretty light by itself, I think around 280lbs before people/gear. Here's what I have in the boat.

- Boat - 2003 Tracker Guide V14
- 20HP 2013 Mercury 4-stroke engine with 3 blade 10P prop
- Minn Kota 55lb Transom mounted electric motor
- 1 Large deep cycle marine battery (27 I believe)
- 1 6 gallon fuel tank 70% full
- some fishing gear (about 10 lbs worth)
- 1 anchor (10lb)
- 2 people (total 340lb)

The main variable that I think might be killing me is elevation. I live in Colorado and testing it out I was around 4800ft elevation. I know elevation is a power killer, but I didn't think it would be this bad. I'm going to try installing the SE 200 hydrofoil to help it get on plane faster. I don't have a tachometer so I'm not entirely sure if the engine is running in the perfect RPM range, I suppose that might be worth the purchase.

Any other recommendations? Should I only expect 21mph max speed at this elevation?

Should I just sell the 20hp and go for a slightly larger due to the elevation? It's very close to being doable, so maybe tuning/hydrofoiling this one will do the trick?

Any help is much appreciated.

 

[dwco5051]

At 4800 feet you would be putting out about 17 horsepower. That would give you a speed of around 24mph at sea level. Your speed doesn't sound that far off what would be expected. Get one of those 15 dollar induction tachs and once you get your speed/rpms you may find you could get a small improvement with a different prop

 

[jlrosine]

Thanks for the suggestion. I'll try to do that over the next few days. I'd probably be fine with 21mph if it gets on plane faster, hopefully the hyrdofoil will help with that (from what I've read it does).

 

[Sea Rider]

Nope an hydrofoil won't cure the patient, before investing on one, order an induction tach, would recommend the Hardline hour/tach model HR-8061-2, cost bit more than any other but way to go for, check Iboats, Amazon for them. Once installed got for a wot run as previously described and report the max achieved rpm to check how much under rpm the motor is revving at from its max rpm factory stated. Rejetting the carb for that altitude along a less pitch prop will do the trick and forget all about installing a hydrofoil...

Happy Boating​

 

[JimS123]

A Doelfin hydrofoil will certainly help you plane easier and the investment will certainly pay off. Buttt, it won't cure your loss of HP nor get you running faster.

The caveat is that for a foil to work properly the motor height must be adjusted to optimize your footprint in the water.

Add the foil, tach it out, raise the motor so the AV plate skims the surface of the water, prop it accordingly and you'll have the optimum performance with your rig.

 

[RMClark]

I think your speed is about what I would expect based on my limited experience. Some data points:

I have a 2021 20HP Mercury Four Stroke on my 14' Lund. When I had it out last week (just me, not fully loaded) I got 23.5 MPH at WOT on a smooth lake with no wind.

When I've had it fully loaded under similar conditions (two fisherman), I got 22 MPH at WOT.

Last summer, at a resort on Lake of the Woods, I rented an 18' Lund Alaskan with a 75HP Evinrude. Two fisherman, and we weren't shy about loading it up. That particular boat was well-equipped and felt heavy. That boat reached about 29 MPH on smooth water at WOT.

 

[reelfishin]

I don't know if this helps since I had an older two stroke but at sea level, on of my previous boats was as follows.
1986 14ft Grumman SS aluminum boat (Open boat, flat floor, center livewell, rear bench, and pilots seat and controls ahead of middle by about 18". Middle seat was stand alone with a livewell beneath. Rear seat housed one battery and a person in that seat could not reach the motor tiller.)
1985 Mariner 15hp 2 str remote with forward stick steer controls.
one group 27 battery/one group 24 starting battery
two 6 gallon tanks of gas
two plastic seats with swivels atop boxed aluminum bases.
5lb anchor and line
Mercury Thruster Bow Mount trolling motor.
me at about 270 lbs back then.
I would top out at 22 mph off the trailer.
I added a Doelfin to the motor to help get on plane faster. It cut down on fuel use, got my up on plane, both faster and higher out of the water and kept me there longer slowing down. but I lost 4 to 5 mph off my top speed.
A prop change helped but cost me fuel. I went back to the original prop.

I discovered a few things about that boat in my years using it, first off, it planed out and got the best top speed with more weight moved forward.
I could gain as much as 3mph simply by moving the one battery to beneath the middle seat, and the second battery up front near the trolling motor on the bow. I moved the front seat and stick steer forward about a foot, the max the cables would allow, and moved my cooler to the front deck. Even then simply standing up and stepping a foot or so forward would increase the speed a couple mph. The most I got out of it with the 15hp running with two half tanks of fuel and me standing toward the bow manning the steering stick and throttle out of the front seat, was 27mph on the GPS. That was also with the lowest pitch prop I could find for that motor running at 5800 rpm.
None of which was really valid info since I moved things around simply to gain top speed as a lets see what will happen experiment. But the fact that I could gain almost 7 mph simply being a halfway down on fuel and everything in the boat shoved to the bow, including me.
One of the biggest issues caused with the Doelfin was aeration of the prop, in turbulent water at full speed up on plane, it would often lose grip on the water and over rev. at first I thought it might be a hub issue but removing the Doelfin stopped it. It was worse with the higher number pitch props.

When I bought that boat, it belonged to the owner of a local tackle shop, he was also into racing small pickle fork boats. Someone who knew him said he bought the 15hp and tore it apart day one and made some changes both in the carb and in porting. I never knew for sure if that was the case, but it was notably faster than most other 15hp powered boats I saw on the water, most being a good deal lighter than mine.

Fast forward about 10 years, I happened upon another boat, same hull, no motor. I slapped a used Evinrude 25hp on it with a tiller, tossed the livewell, stick steer, second fuel tank, trolling motor, and anything else I didn't need.
With me sitting at the rear, with a 6 gallon tank pushed forward at my feet, and no batteries on board, the best I got was 19 mph, a tiller extension and moving forward got me 21 mph. But keep in mind its on modern fuel, and with little to no real weight in the bow. A Doelfin added to that boat really helped it get on plane and it didn't lose any speed, it even gained some speed on choppy water but I never messed with the setup beyond that.
I moved the same set up to my 14SF DLX Starcraft a few years later and on that boat, with a full floor, split bench, and livewell, the manual start 35hp would top 25mph easily and lost speed with more bow weight.
Looking back, a little older and a little wiser, I think it all had more to do with the hull angle to the water while on plane than with hp. The more boat you get out of the water, the fast you will go. The drag caused by the water alone is the biggest enemy to top speed in a small boat like that. After that its wind resistance and weight.