2005 Merc 40m mods for river racing

[cory]

Here's the pics of the bottom of the boat that I promised. Sorry for the late response. I tried to take the best pics I could with the boat on the trailer. Let me know what ya'll think about where to put the angle aluminum and how wide the pad should be. I have a bunch of .080 aluminum around the house and I could get some 1" or 2" angle to make the "air entrapment" that ya'll speak of. Thanks.

Cory

[cory]

My strakes are about 6" apart center to center. I am gonna weld 1" aluminum angle to each runner immediately outside the center making my air trap 12" wide. Then weld my flat piece of 1/8" aluminum plate between the two pieces of angle all the way to the front where the the hull starts upwards. What yall think? Think that pad would be too thin?

[Cubman]

TTT

Any more advice on setting up an aluminum boat? I've got a 1648 with about 7* V on the bottom with a 70hp Johnson tiller. How much setback should I start with? I need to run a prop with a hub since this is a duck boat, but should I run a bow-lifting or stern-lifting prop?

[Cajun]

Cory, right now, you are prop limited. First, if you want to gain the most mph for the $, talk to Ron about a prop. With all respect due to PowerTech, that is not the best prop selection for what you are trying to do. Try a Yamaha Black Painted Stainless Steel on that rig, you will see 2-3 mph difference. If you are planning on surfacing a prop, you will need much more pitch, as Ron could explain much better than I. Playing with aluminum hulls, I have found the optimum setback is 10". After 10" the gain is not proportionate to the setback. From 10" to 18", the gains are very minimal, after 18", the gain rise a bit. That said, 18" is not practical for a tiller.
I know we run different hulls, the Edge bottom is designed to run. For reference, I run an Edge 556, a 15'2" long, 56" wide bottom, aluminum hull, weighs 352 pounds empty. I run a 61 ci Mercury 4 cylinder 4 stroke, EFI, set back 10" with a hydraulic lift plate. The motor has a 60 ecu and makes 64hp@ 6249 rpm. With me @ 205#, a 12 gallon fuel tank, a large starting battery, the hull runs 52mph at 6250 rpm. With another 200# man in the boat, the rig runs 49mph. I run a Yamaha stainless averaging 16.5 pitch. I know if I wanted to play with "race" props, the boat could run much faster, but, I'm gettin too old for unplanned swimming trips.
Please excuse the poor driving, this was the maiden voyage for this rig, took a while to figure out her quirks.

http://s126.photobucket.com/albums/p...rent=good4.mp4

[Cajun]

And now the motor with her stripes back on:

[Cubman]

Cajun,

Will a jackplate on an aluminum boat do much for speed or is it primarily for shallow running? Is there a hub available to run this yamaha prop on a V4 OMC (13 spline, 4.25")?

Thanks

[Cajun]

Cajun,

Will a jackplate on an aluminum boat do much for speed or is it primarily for shallow running? Is there a hub available to run this yamaha prop on a V4 OMC (13 spline, 4.25")?

Thanks

The jackplate is primarily to allow you to raise the engine. They were designed for shallow marsh fishermen. The speed gains are moinimal and a byproduct of raising the engine. I think they sell a yamaha black painted stainless for that will fit the V4.
D

[Cubman]

Sorry for the elementary question, but if I operate in water no less than 3' deep would I be better served to just raise my motor on the transom until I loose water pressure or cavitate?

[Cajun]

You could, but it doesn't give you the adjustability of a jackpklate. Most jackplate have 3" lift adjustability built into them. If you are wanting to go faster and faster, use every little advantage you can get. Because I do, and have tested so many 60hp and under props for a certain manufacturer, I have a hydraulic lift, so it's easy for me to test diferent props and report accurate data. My 10.25" diameter Quicksilver Vengeance will run about 2" above the transom, my STOCK 10.25" diameter Yamaha will run about 3" above the transom, my modified 10.25" diameter yamaha will run about 6" above the transom as will my Quicksilver Trophy Sports, my 12" diameter quicksilver cleaver will run 8" above the transom.
Di

[Fastjeff57]

Cubman:

You need to run your boat for a few days with the motor raised WAY up there. If you do, you'd find that the simply act of planing off takes on a whole new meaning! The prop will cavitate like mad, shaking the entire boat (and doing no good for the transom and suspesion components) until you finally nurse her on top. Do that a few dozen times and you'll be delighter to lower her back down there, even if you have to give up a few miles per hour!

Jeff (been there, done that, changed back)