Speed of a 21ft Mariner

[bayonnebandit]

It’s been a while since I’ve posted on here. Hope everyone is well and and are enjoying their boats.
This year I made a second overhaul on my Mariner. It’s a 76 that was my fathers (he passed away when I was young)

As part of the overhaul I splurged and bought one of the last Etecs ever made. It’s a 140hp G2.

My question is this, what speeds should I be seeing on it. I am coming from a 90hp Etec from 2004 that I could get up to 37.5mph. With the new engine I get 46mph. Don’t get me wrong that’s plenty fast, but it just seems that I should be going faster. The engine is a beast and its propped right and hung at the right height. Just seems like the hull is holding it back. Like the rivets are little claws in the water or something like that. Anyway, just wanted to get some of your opinions.
Attached are some pictures of the build

 

[MNhunter1]

Beautiful Mariner! Not sure I have any info for you on the expected speed, but either way, she's a beauty.

What did you use on the deck and how is it holding up?

 

[bayonnebandit]

I’m just wondering if I was expecting something that wasn’t possible. I thought that big of a jump in horsepower would translate into more than about 8mph but there is a lot at play… engine’s heavier for one.

Thank you. A lot of work but getting to enjoy the fruit of your labor is nice for sure.

The flooring is an imitation of what’s known as Seadeck that I bought on eBay. It’s called EVA foam and isn’t tremendously expensive little under $250 to cover the boat. Comes in various colors and shapes. It has its pluses and minuses like everything. Pluses are: nice looking, sound deadening, stain resistant, and cushioning. Minuses are: little tough to keep clean unless you are anal about it and poor impact resistance (you are going to puncture it if you drop an anchor on it). The best way to describe it is it’s a mat made of the soles of sneakers … that super dense foam stuff. It comes in sheets so I planned it out where I have the aluminum strapping on the floor cover the seams. Looks nice and allows me to pull up and replace a section if something happens.

The original deck below I made out of trex rim board so that it can’t rot.

You can see in the photo I was originally going to go grey but the mahogany color surprisingly looked real.

 

[Alumarine]

Nice boat!
To answer your speed question you can use a prop calculator.
You need your gps speed, rev's and gear ratio.
If you provide those someone here can help you out.

 

[bayonnebandit]

Cool. That would be great. I get 46.3 gps running a 19 pitch (14.5” diameter), with a gear ratio of 2.08:1 and rpm at 5750.

I’m told on an Evinrude forum I’m on that I could go to a 21” which would bring me down to about 5400 and right in the sweet spot of the engine horsepower range. That being said, these new props arent inexpensive so I’m not sure if it’s worth it.

 

[Alumarine]

Cool. That would be great. I get 46.3 gps running a 19 pitch (14.5” diameter), with a gear ratio of 2.08:1 and rpm at 5750.

I’m told on an Evinrude forum I’m on that I could go to a 21” which would bring me down to about 5400 and right in the sweet spot of the engine horsepower range. That being said, these new props arent inexpensive so I’m not sure if it’s worth it.

I'm not a prop expert but that works out to 8% slip which I think is good.
If you went to the 21 at 5400 with 8% slip you would only improve speed by 1mph.

 

[dwco5051]

Boat speed vs power is not a a linear relationship. If so by increasing your power by 55% would result in a speed of about 58 mph. The truth is calculating speed vs power for a planing hull is very complicated depending on a lot of factors. Even the wind resistance force is quadratic meaning that if you double the velocity the force is four times as much. I looked up a couple of sites for calculating speed and the math was more than I carried to tackle 60 years after I got out of college. My gut feeling is that 46 mph may not be that far off.

Planing Hull - an overview | ScienceDirect Topics

www.sciencedirect.com

Planing Hull Calculations Description, Crouch's Formula

 

[dwco5051]

Just ran your new speed squared divided your old speed squared and the result is almost the same as you power increase.
140/90=1.55
2116/1406=1.50

 

[The John]

I cant comment on the motor information you are looking for but you have a beautiful boat. Im working on my 75 marine but it wont look as nice as yours, you did a great job!

 

[bayonnebandit]

Thank you for the compliments. Makes all the curses and bloody knuckles worth it

Seems to be that I was expecting a little too much from the upgrade. I was hoping to hit 50 just to be able to say it. Oh well. She’s plenty fast, and is a rocket out of the hole. Here’s a video of the first splash with the new engine

 

[Moserkr]

Makes me want to paint more of my boat white!! Lol. She looks great! Probably flys out of the hole and I bet thats the biggest difference between the two motors.

 

[Watermann]

Your hull is not designed for speed, with a dead rise hull there is a hump to get past which is around 45 MPH and without a padded hull like boats made for speed have you need a bunch of power to break past that. I barely can with my Chief that has a 205 HP 4.3L V6.

Part of the problem is guys that lie about how fast their boats will go with a given motor which makes some think their boat should go faster.

My 18' SS with a 140 Merc would go 45 MPH by the GPS and there was no breaking over that hump.

 

[DWbaseball]

Nice Mariner! Looks great with the faux wood foam and you are flying out of the hole with the new 140.

I am interested in your bow pulpit setup as I have thought about something similar on my build. Does that work as a permanent Anchor storage mount for you? Can you let me know how you use it in practice? Any more pics?

 

[bayonnebandit]

Ha, I know well about other boaters telling tales about speed. My friend just bought a new boat this year and he called me saying he hit 54. I watched a boattest.com review of the same boat and they hit a top speed of 46. I know they aren’t always accurate in their reviews but there is no way there is an 8mph difference unless he was driving down rapids . You are right about that 45. It kinda hits there and then nothing. Thats why I asked the question in the first place. Thought something may be wrong in the setup.

baseball … I have anchor storage underneath the seats at the front. The pulpit gets the anchor further out so the rope doesn’t hit against the hull when the boat floats over it. There is a groove in the front that keeps the rope nice and neat. I suppose you could keep the anchor out there, some boats have that setup with a motorized anchor line but I don’t. Here are a few pictures I drummed up. I’m not by the boat so if you need more let me know and I’ll snap a few over the weekend.

 

[DWbaseball]

Thanks, I see the notch there and good intel about the anchor rope rubbing on the hull.

 

[jdvasher]

Its like cars and 150mph. Once your there it takes ever increasing HP to go just a little faster. With vehicles is mainly the aerodynamics so I would have to think hydrodynamics are playing a very similar role here. Very nice boat BTW.

 

[The John]

Nice Mariner! Looks great with the faux wood foam and you are flying out of the hole with the new 140.

I am interested in your bow pulpit setup as I have thought about something similar on my build. Does that work as a permanent Anchor storage mount for you? Can you let me know how you use it in practice? Any more pics?

Depending on your anchor setup you can use lee lock or miller bracket. We use this style of anchor here in the PNW. We use buoys to pickup anchors that would otherwise be very hard to dislodge from the bottom of the Columbia river.