Looking for some speed comparisons. 1756 G3 with 70hp Yamaha

W

William Rhea D

New member
I just picked up a 2009 1756 G3 with a 2006 Yamaha 70hp. It will run about 33-34mph with just me and a dog. I've tried it with a 15 pitch prop and an 18 pitch with both about the same speed. I was thinking with a 70 it should do a little better than that. It doesn't have a tach so I'm not sure I'm getting full rpms. Working on installing one now. I use it for fishing too and would prefer to be closer to 40mph for some areas. I'm just looking for some speed comparisons for what you guys are running. I'm thinking I may can have some work done on the motor and get a few more MPHs but not sure. Thanks.
 
Not really a good comparison, but my 19'3" Honker, will do 32 MPH, empty with 2 men in it. It has a 1993 Yamaha 60 hp 2 stroke on it.
 
If you are getting same speed from a 15P and 18P there's something seriously wrong.
If any thing the 18 should slow you down
Are you trimmed correctly ?
You could be too deep down also measure the cav. plate at the bottom of hull.
I ran all my duckboats at 2 inches higher (I set a 15"shaft at 17" and my 20" shaft a shade over 22")
 
Thanks for the info. I have played with trim while running. At WOT I trim up to just before the boat starts porpoising and that's how I'm getting it to about 34 mph. I honestly haven't checked (and didn't really know to) to height of the cav. plate. I will check the height when I get home this afternoon. I'm not understanding what you mean by setting a 15" shaft at 17" etc...

Edit: Just FYI it also has a 21 gallon tank in the rear and 3 batteries (2 for 24v trolling motor). I'm sure that isn't helping. I can move 2 of the batteries up front but there isn't any room to move the tank to the front.
 
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I mean I had the motors mounted 2 inches higher then the shaft length.
You could also not have the right angle bolted to the transom?
When I went up 2 inches in pitch I dropped a little over 400RPM, you should see the same difference between the 2 props and maybe more
 
there have been some good comments and advice given.

1) you have to get a tach installed. without that you are shooting in the dark on motor setups
2) that boat and motor with essentially an empty load (you and the dog) should easily run in the mid 30's; with a hunting load; in the lower 30's
3) the cavitation plate should be at 1" to 1 1/2" above the bottom of the boat.
4) you need to know what WOT spec is for that motor probably ~5500 RPM's
5) with a load; the 15P prop is probably going to be close to what you need.
6) you need to move as much weight forward that you can. moving batteries is a start.

once you get a tach and the motor height set. give us a report and we can have further discussion
 
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Thanks for the help so far guys. A little info from investigation last night: motor cav plate is about flush with the bottom of the boat. See pictures. The picture with the straight edge is a little deceiving from the angle I took it but the cav plate is within 1/8" of being flush with bottom of boat. There is about 1-1/2" available with the mounting holes to raise the motor. I will work on that and report back once I have a tach installed and some usable info. If I want to get a spare 15p prop is there any sense in spending the money on anything custom/worked or is a standard prop just as good for what I'm trying to accomplish?
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Yes on the tach. I spent quite a bit of time looking at tachs because I had to replace mine this winter. There are a TON of knockoffs out there that look just like the originals. Sendec and tinytach seem like the trusted originals. I have had and like the sendec ones, since they run on one wire. SenDec is owned by GCI and they don't sell direct/retail anymore, but they recommend "Hardline" as a seller (they badge the Sendec to "Hardline"). I bought a hardline "HR-8061-2" off amazon for my motor since it is programmable and I have a non standard firing pattern, but you may have a standard firing pattern (a programmable unit will handle that too). Anyway, they are cheap ca. $30 and you want one to figgure out your performance issues.

From the looks of your setup you could go up one or 2 holes for optimum speed (1 inch or 2 max), but you are flirting with ventilation/aeration on turns and in heavy seas if you get up much above what you have. Standard high performance is having the motor a little higher than even with the hull. For a duckboat, I would like only barely slightly above the bottom for versatility's sake.
 
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I don't know where the OP is located and what kind of waters he is trying to run in. I am in Iowa and my set up is strictly for duck hunting and mostly on marshes. therefore I try and set the motor up as high as I can (cavitation plate is 2" above bottom of boat) and I run a CMC H jackplate. this is a 60hp on an 1860 with hard sided blind with a full load of 3 doz Canada blocks, 7 dozen mag duck blocks, heaters, ect., ect. gas tank and one battery is all the way to the front. this will run approx. 31 to 32 mph with a full load, three guys, and the dog. I am running a 13 P alum prop. at 5500/5600 RPM WOT. I am a big believer in Alum versus SS because of hitting stumps/bottoms/rocks I would rather eat up one or two props a year than have the prop shaft or lower bearings get toasted.

I agree that if you are typically running large open water; then set the motor up with the cavitation plate even or 1/2" above the bottom. You need more bite/control in heavy seas than what I experience on cattail marshes
 
Wanted to give a quick update on this. I ordered a Yamaha 6y5 tach and just received it end of last week. I haven't installed it yet but plan to this week. I did go run the boat once I had raised the motor 1.5". I was able to get 36mph with the 18 pitch prop and 35mph with the 15 pitch prop. I will run it again once I install the tach and report back. Thanks.
 
I have a 1754 Polarkraft tunnel with 16 inch floatation pods welded on the stern, a vent in the tunnel, a hydraulic jackplate, 4 bladed stainless lifter prop (and a 3 bladed Yamaha factory prop) and a Yamaha 50 hp with the restrictor plate removed & reset electronic brain (so it is a 60 hp motor). I've never gotten it above 34 mph with a bunch of tweaking. I really don't think you'd want to go faster in a flat bottom tin boat except on glass smooth days. I have a 19 foot Bankes also with a 115 hp Yamaha with a 21 pitch for when I'm not carrying guys or heavy loads of decoys. My top speed is 45 mph with wind, tide and current and that speed is crazy stupid fast for a duck boat.
 
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