'duck' boat--tuning advice?

[junkyardwarrior]

I'm an experienced outboard tech (Yamaha only up to about 100 HP), but a noob when it comes to getting the most out one. Normally we just hang the motor on the transom, screw it down and let it go. And 99% of people are happy with that.

What I have is a customer with a 1542 Grumman flat bottom "duck" boat. The engine is a early 2000's model 4 stroke 25 Yamaha. Good motor. We generally never see them in the shop unless they've been sitting all year. He is trying to get the most out of his rig. He typically doesn't carry much gear. A shotgun, some shells, about 5-10 decoys and the usual jackets. No heavy duck blinds. Loaded between the operator's weight and gear, probably 400 lbs at the most.

He complains every year that his motor is slow. I've run it at the river and GPS'd it at 26 mph max. I thought that was respectable, however, he feels like he could do better. It has a stock 9 7/8 x 11 1/4" Yamaha 3 blade aluminum prop and the engine was about 5600 at 26mph.

My customer has been loyal, but he's considering buying a new 2 stroke (probably Etec if I had to guess....) and I want to show this guy that I can make this thing run 30 (hopefully more but I set a goal of 30) with his Yamaha.

 

[muskrat]

Re: 'duck' boat--tuning advice?

You go up in pitch two inches you might see two to three mile anhour more.

 

[robert graham]

Re: 'duck' boat--tuning advice?

26 MPH at 5600RPM's sounds about right. That flat bottom makes a lot of drag! Sell him a new Yamaha 40HP and he'll be more happy!....maybe

 

[junkyardwarrior]

Re: 'duck' boat--tuning advice?

26 MPH at 5600RPM's sounds about right. That flat bottom makes a lot of drag! Sell him a new Yamaha 40HP and he'll be more happy!....maybe

Oh he would be tickled pink with an F40!! 3 cylinder, power tilt, etc. The issues are this: The boat is rated for 25 HP max. And many of the duck hunting areas locally are lakes/rivers/marshes that are 25 HP max. AND...they're policed. In this state, any modifications to outboards that would increase engine's rated output above what was originally rated for are illegal-and yes the fish and game people DO police it. At one time I had a 1548 War Eagle with a 3 cylinder 25 Yamaha (manual start only 25MSHU2) with some Hydrotec mods (tuner, head, flywheel, carbs, ported block) that would kick booty. However fish and game guy recognized the "different" looking head (looked stock other than you could tell that it had been off), the prop, and the fact that I was running across the swamp at about 43 mph...and gave us a stern warning about the "new" (at the time) law. People still modify them though. We can do props, etc but nothing to increase the engine's horsepower output. Well legally that is. Guys are still using Tohatsu Mega's and getting 50+ out of them.

Still looking into other things that I can do to this F25 without opening up the engine. I might be able to sell him a PT-35, but only if it'd help him. I suppose I could raise the engine some while adding tilt at the same time? But the weight of the unit (around 30 lbs) concerns him a little. Not to mention that it moves the tiller further to the rear.

 

[robert graham]

Re: 'duck' boat--tuning advice?

Well, good luck with the hot-rodding, but seems like a lot of trouble for a few MPH top speed increase...he must be in a hurry to kill some ducks!

 

[junkyardwarrior]

Re: 'duck' boat--tuning advice?

I've never known him to be in a hurry. However, ducks can't be hunted until daybreak. The boats (if used) cannot leave the ramp or marina until 4:30. Most are in the water at 4 am, then at the tick of 4:30:00, they're full speed ahead to get to their hunting area. First one to get to a particular area gets that spot.

 

[Home Cookin']

Re: 'duck' boat--tuning advice?

Sounds like the sparkle boys are running the duck hunting there.

He's not going to solve his "problem" when he's committed to the boat and has the top end motor. the prop change will give him a couple points but I can't see spending $100 for 2 mph.

One suggestion is to see how he's loaded and work on getting the boat, when it's on a plane, as flat as possible. Move the fuel forward, battery too if he has one (or just don't use a battery), etc. and anything large for aerodynamics. Might not make that much difference but if he thinks it does, you're a hero.

I've never known him to be in a hurry. However, ducks can't be hunted until daybreak. The boats (if used) cannot leave the ramp or marina until 4:30. Most are in the water at 4 am, then at the tick of 4:30:00, they're full speed ahead to get to their hunting area. First one to get to a particular area gets that spot.

 

[steelespike]

Re: 'duck' boat--tuning advice?

You could try raising the motor to a point just before venting becomes a problem.
Also perhaps a prop like a Turning Point Rascal.would allow more height.
As suggested the Jon isn't exactly a fast bottom.
Besides the poor shape it probably has 4 or 5 keels adding drag.
Perhaps the right prop will allow you to get the bow up and have less boat in the water.
Is the bottom clean and smooth?

 

[nwcove]

Re: 'duck' boat--tuning advice?

bang the dents out of the hull, a couple of coats of wax.....and presto, a few more mph.