Speeds to expect on modified tin boat?

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Taxin_That_Bass
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Speeds to expect on modified tin boat?

Post by Taxin_That_Bass »

Hey guys, just joined the site, love the fact that its all about tin boats. First off i'm going to pre-apologize about the length of this post.
Quick background on myself, bass fisherman from La Crosse WI, have always owned a bass boat for tournaments and a tin boat for fun fishing in the sloughs. Sold my bassboat last year as well as my 14 monark. Got a steal on a 1972 Polarcraft 16ft flat bottom with coast guard nose with a 1981 evinrude 35hp. I wanted to convert it into my "tin bass boat", i knew going into this that i would add significant weight and would lose speed. So...

i added a large deck up front that runs from the front of the boat and covers the front bench seat, with recessed trolling motor pedal, tackle compartment that stores a tote with tackle, life jackets ect. Also added side lockers for storage that run between the middle and front bench seat that store one grp 31 battery, noco on board charger, anchor and other misc items. I added a back deck that covers from the transom over the back bench. Also added floor between back and middle bench seat and middle and front bench seat. Transom has 6 gal gas tank and another grp 31 battery. I have a 70lb maxxum bow mount trolling motor up front aswell. All of the decking, floor, and framing is made from plywood and 2x4. Obviously this is much heavier than aluminum, I considered using aluminum but at the time it was just way too expensive (may to re do it at some point).

Anyway, so i have added a quite a bit of weight to the boat. I also added a tachometer to the motor, by myself i am getting about 24 mph gps at about 4500 rpm wot with semi beat up 10x13 aluminum prop (edges on two blades are chewed a bit). Two people drops to about 20 or 21 and dogs to get on plane.

Questions: 1) 24mph on a heavily loaded 16 tin boat seem appropriate?
2) Do you think a SS prop will help me much?
3) do you think dropping to something like 10x11 to get my RPM closer to 5500 will help much on top end speed? I would think it would help with hole shot at least

Thanks in advance.

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Johnny
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Speeds to expect on modified tin boat?

Post by Johnny »

Welcome Aboard !!

I guess I am too Old School - - - but, why isn't 24 miles an hour enough ????




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Taxin_That_Bass
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Speeds to expect on modified tin boat?

Post by Taxin_That_Bass »

Johnny wrote:Welcome Aboard !!

I guess I am too Old School - - - but, why isn't 24 miles an hour enough ????




.
Haha good question, 2 part answer: 1) I fish the upper mississippi river and it's giant, a few more mph won't make much of a difference getting from point A to point B but it my mind it does :D
2) I just feel like 4500 rpm just isn't getting to the peak point in the HP curve for my motor, so i feel like i'm leaving some HP/speed on the table. If a different prop will help it out, then great, if not than i can put it behind me and go with what i have.

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Johnny
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Speeds to expect on modified tin boat?

Post by Johnny »

our fellow Motor Guru, Pappy is the local expert in the
1980s OMC outboards . . . . he will give you the correct specs.


if you are looking for speed and power - I would try to budget for a 50hp Johnson and be done with it.

my grandmother had a saying . . . "you are wanting too much sugar for that dime"



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http://www.tinboats.net/how-to-build-a-transom/
http://www.tinboats.net/varnish-vs-polyurethane/
All about Primers = http://www.tinboats.net/primer-and-paint-basics/
Paint, Thinners and Applications = http://www.paintingforpainters.com/

1959 Crestliner Commodore 14'
1959 Lone Star Malibu 14'
1958 Johnson 35 RDE-19 Sea Horse
1958 Johnson 35 RDS-20 Super Sea Horse

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DaleH
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Speeds to expect on modified tin boat?

Post by DaleH »

It is not MPH you should be concerned with, but RPMs!

IMHO you are severely lugging that motor and besides not adding oil, using the wrong prop is a sure way to kill a motor.

By my search that is a 5800 RPMs maximum motor and if it were mine, I'd never settle on a prop until I reached at least 5600 when running the boat alone, 1/2 fuel and with all gear typically carried.
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Stumpalump
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Speeds to expect on modified tin boat?

Post by Stumpalump »

What DaleH said.. Skip the stainless.
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Stumpalump
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Speeds to expect on modified tin boat?

Post by Stumpalump »

What is a "Coast Gaurd Nose" ???
1991 18' Valco Bayrunner Evenrude 48 SPL

Arizona

Weldorthemagnificent
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Speeds to expect on modified tin boat?

Post by Weldorthemagnificent »

If nothing else a 10x11 would get you out of the hole easier. I'd stick with aluminum.


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Crazyboat
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Speeds to expect on modified tin boat?

Post by Crazyboat »

I think the rough rule is you gain 200 rpm for each inch of pitch (I may be very wrong). You need to increase your RPM to the max recommended for the outboard which I think is 5,500 with a light load. As you add a fishing buddy your RPM will drop and that's OK.

24 MPH sounds about right and I doubt you'll get much more no matter which prop you go to, if you hit 26 be happy, unless you are willing to drop the weight for another 1-2 MPH.

Taxin_That_Bass
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Speeds to expect on modified tin boat?

Post by Taxin_That_Bass »

DaleH wrote:It is not MPH you should be concerned with, but RPMs!

IMHO you are severely lugging that motor and besides not adding oil, using the wrong prop is a sure way to kill a motor.

By my search that is a 5800 RPMs maximum motor and if it were mine, I'd never settle on a prop until I reached at least 5600 when running the boat alone, 1/2 fuel and with all gear typically carried.
i was a little concerned about that. Can you tell me why it is hard on the motor? Why operating at that point kills motors?

Taxin_That_Bass
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Speeds to expect on modified tin boat?

Post by Taxin_That_Bass »

Also, can you recommend a prop for my setup then? Was looking at the solas 11x9. I think i need a significant drop in pitch to get my rpm where it needs to be

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Stumpalump
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Speeds to expect on modified tin boat?

Post by Stumpalump »

Post pic of your original beat up prop.
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edlacy
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Speeds to expect on modified tin boat?

Post by edlacy »

Taxin_That_Bass wrote:Also, can you recommend a prop for my setup then? Was looking at the solas 11x9. I think i need a significant drop in pitch to get my rpm where it needs to be

You're lugging it.

You wouldn't drive a manual transmission car 15 MPH in high gear. You're doing the same to your outboard.
As was stated above, you want 5300-5400 RPM @ WOT or you'll never know the full potential of you motor. As well, you're shortening the life of the motor. Those Evinrude/Johnson motors are real work horses, but any motor can only take so much abuse. Running your motor at low RPM is abuse.

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LDUBS
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Speeds to expect on modified tin boat?

Post by LDUBS »

Crazyboat wrote:I think the rough rule is you gain 200 rpm for each inch of pitch (I may be very wrong). You need to increase your RPM to the max recommended for the outboard which I think is 5,500 with a light load. As you add a fishing buddy your RPM will drop and that's OK.

24 MPH sounds about right and I doubt you'll get much more no matter which prop you go to, if you hit 26 be happy, unless you are willing to drop the weight for another 1-2 MPH.
Aw shucks, never mind. I should have read the whole thread -- :|
Have Rod - Will Fish

Taxin_That_Bass
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Speeds to expect on modified tin boat?

Post by Taxin_That_Bass »

Stumpalump wrote:Post pic of your original beat up prop.
I will try to get a pic of it tonight. I hate buying props without trying them, but i might order a 11x9 solas and see what that does.

I'm pretty confident my rpm measurement is correct, but just to confirm, i got one of those induction tachs where you wrap it around the spark plug wire. There are three settings on it, 1 pulse per 1 rev, 2 pulse per 1 rev, 1 pulse per two revs. I at first set it to one pulse per one rev but it was obviously way too high, i changes to 2 pulse per 1 rev and then the numbers looked more believable. I guess some of these older outboards will spark when the piston is at bottom dead center as well as TDC?

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