# alternator drag vs engine rpm.



## bptjr (Dec 14, 2014)

Anyone try disabeling alternator to gain rpm? Im running a honda bf9.9d and trying. to get one more mph to hit my goal
.


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## JMichael (Dec 14, 2014)

I must be missing something here so I'll bite, how would that make it faster.


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## Boat2fast (Dec 14, 2014)

Too many strokes...need to lose a couple.


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## bptjr (Dec 14, 2014)

Probably should have been clearer about what i'm doing. Close to the end of a need for speed project. I set a goal of at least 20 mph. One more willdo that. If i can gain any rpm at all it will help. Any drag on motor costs rpm/ speed. In this case the magnetig drag of a charging coil will cost some ,even if its minimal.


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## KMixson (Dec 14, 2014)

I would think waxing the bottom of the boat would be an easier way to gain 1 MPH.


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## Pappy (Dec 14, 2014)

Waxing the bottom of a boat for speed is both false and ancient heresay. Will do nothing but slow a boat down. 
These days (for a fiberglass hull) straightening and then sanding the bottom to a 400/600 grit finish and leaving it that way will produce better speed. All trailing edges should be filled and sharpened to force the water to leave the hull cleanly. The sanded finish builds up a tiny boundary later of water over the boats running surface that the passing water travels over and past with less friction. 
However. 
If you are serious about running a little faster for less work you can jack the engine up a little and probably gain what you are after. Or...........
Change the propeller to a faster design. or......
Have the propeller sent out to a performance prop shop and have the blades thinned and modified. The latter will give you the most bang for the buck. Know your exact average speed and RPM when you deal with a performance prop guy. That will be your baseline. All variables in the boat will have to be kept the same(eliminated) for these changes in order to verify gains.


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## bptjr (Dec 14, 2014)

Already did jack plate props trim weght reduced pivot lss transducer moved what weght is left to help lift changed starting battery to lighter one im running ot of things to do while still keepng it a fishing boat. Just wanted more spees


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## Y_J (Dec 15, 2014)

Isn't that a lot of stuff to go through for just 1 mph?
Guess I'm missing something here.
Have you tried leaving all your gear off the boat while trying for that extra?


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## bptjr (Dec 15, 2014)

All of this started at 13 mph. Now at 19 . My goal is at least 20 with boat loaded normal. Its a 1548 alumacraft allweld with 9.9 honda. Its only got down to needing 1 more mph afterall this work. May be time to put me on diet,instead of boat.


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## Boat2fast (Dec 15, 2014)

Your 1548 welded boat is a lot heavier than a 12' riveted rowboat. I think 19mph with a 9.9 4s is a pretty respectable achievement.

That said, Pappy had the best suggestion. Wet sand the bottom really smooth. I heard this trick from a crew coach. It will minimize the boats drag. The drag increases as the square of speed. This can free up a lot of power for building more MPH. It is the only area you haven't already visited.

If you haven't already tried it...place a 3/4" shim between the top of the transom and the mounting clamp. This so the engine is elevated a little. If your transom is already 16'' tall like some are, then this may go a little too far. Prop ventilating means you went too far here. Sometimes the prop will vent a bit until the boat pics up enough speed to hook it back up. Ride it out with a delicate hand on the throttle and see if it hooks back up. Don't over-rev.

If you disconnect the battery you will eliminate the alternator load. It will be a tiny gain at best. You will never see a difference from that.


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## lckstckn2smknbrls (Dec 15, 2014)

Try dimple tape on the bottom.


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## bptjr (Dec 15, 2014)

thanks to all for the helpful ideas. today I tried changing props again , from solas Saturn 9.25/9/3/ss to solas Saturn 9.25/10/3/ss. it lost 330 rpm and 1 mph. possibly somewhere in between? 9.25/9.5/3/ss ? probably not cost effective. im currently jacked up 5.25 inches above transom with a vance 6 inch jack plate. still peeing water normal. went from 2 trolling mtr. batts. to 1 (this should be ok ,I usually only fish aprox. 4 hours a day) I took cranking batt. out &replaced with smaller one. moved front mounted t/m batt. a little further back. these changes have got me from 13 mph to now at 19mph. im thinking the jack plate might be dragging water,but raising front half then lowering back half might help? so close to 20 I can almost see it!!


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## Boat2fast (Dec 15, 2014)

Sometimes I get so wrapped up in the next 1/2mph...I forget to have fun boating.


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## turbotodd (Dec 16, 2014)

Is the Solas the only ones you've tried? Lots of props on the market and lots of them much better than Solas, but not being familiar with 9.9 and especially Honda, Solas may be the only option. Don't know. Messed with some 15's and some 25's, 4 stroke and 2 stroke both and always found that the Solas was a good "all around" prop but they were not great at any one particular thing. They gave up speed for holeshot and midrange, which is why I consider them a "all around" prop. Might try Turbo, they have a decent selection. I don't know if you'll get 1 mph, however. The little motors are a lot harder to squeeze speed from than, say, 90 hp+. On the bigger motors, 1" of pitch roughly equals 200 RPM. On these little motors, 1" of pitch equals a bunch more RPM. On my 25, about 500 RPM +/- 50. Things change drastically when you get down this small on HP.

Hull mods can gain a TON of speed. Done right, you may find 3-5 mph after the correct prop changes. I've done a war eagle hull long ago, 1548 LDV. It looked decent with the naked eye. Flipped it upside down and ran a straight edge longwise and found all kinds of imperfections. They do a good job of minimizing weld warpage but you can't eliminate it in mass production. Well you can, but it takes a lot longer to prep and finalize the product, which slows production processes. After straightening a lot of the warpage and then final sanding with 400 grit, I was astonished to find that it was worth 4.7 mph on average. On the back of the boat, where the transom is welded to the bottom, some boats have a "ridge" there, where there may be a weld bead. Do not remove it. You can take it down a little at a time until the boat starts seeing porpoising, then stop. Conversely, you can add that bead back on with JB weld to control porpoising, but it'll also add just a little drag. Removing it a little at a time can find you .5-1.0 mph depending on how bad it already is. If you find a rocker in the hull, beat it down flat the best you can. If you find a hook, you'll have to beat it out from the inside if you can get to it. That or lots of filler but filler adds weight. A little bit of hook at the very back of the hull might be fine; as it helps with porpoising. Hook is a "dent" from the bottom up, and tends to suck the boat down onto the water. "Rocker" is dent from the top down and causes all kinds of things to happen depending on the severity and location. Oddly enough, some boats dont' have a bead at the back and no rocker or no hook. I've seen guys (the duck hunter boat racers) take a brand new boat and remove the motor, flip the boat over, and go to town on it with a hammer to put a hook in it to stop/slow the porpoising. Makes me cringe.

The alternator, on a 9.9, doesn't draw much power. A tiny bit maybe but I seriously doubt you'll see any difference. Some guys in the 25hp stuff out here will remove a perfectly good working charging system and put a manual start flywheel and manual start pulser/trigger coil plate assembly to free up less than 1 hp. Remember, we're talking about ~15A charging system. Some of the big motors with 50A+ charging systems can benefit a lot more, but on the 9.9, not worth the effort. Wanna try it? Disconnect the charge coil from the harness if you can, and try it. Doubt you'll see anything noticeable.

Have you adjusted the valve clearance? Helped on mine. On mine, I tightened the clearance a little lower than spec, picked up about 50 RPM in similar weather conditions. From .009" to .006". This effectively makes the cam "bigger" by a tiny amount.

Can you do anythign with the air intake? My 25 had a long intake horn that makes a 180° direction change. The throat of the carb intake faces toward the front of the motor but the intake horn/silencer comes off the carb and makes an immediate 180° turn and then faces the rear. I removed it, and lucked out finding a little bitty intake funnel that fits the little metal retainer that normally holds the factory intake horn on. Was worth almost 200 RPM but I also had to re-jet a little leaner (from 115 to 112).

Kind of a non-reversable mod, but modding the carb to methanol is worth a ton of low end and mid range power, and a little top end power too but you notice the torque more than the horsepower. On my 25, with only a methanol carb change (with it's modded intake funnel), I went from 29.6 mph average to 33.9, no other change. But finding methanol at the gas station is a big challenge. I get it at a place that sells race fuel in bulk since both cars run on it. Also E85 is worth a little power but modding the carb is not easy with Meth or E85. Takes lots of time. Meth, you'll need about 65-75% more fuel flow thru the carb. E85 I am not familiar with.

Can you play with ignition timing any? Mine, I slotted the pickup coil holes and adjusted it exactly 1.5° advanced, which is all I could get by slotting the holes. Motor is more responsive, starts better, and maybe got a quarter mph or thereabouts. Did not test MPH, just a guesstimate. Every motor will be different; mine just happened to like it. Plugs don't show anything to be concerned about.

Make sure your throttle is opening all the way. Have run into that with Yamaha stuff. Also, I did a 9.9 once that the guy was complaining of lower than expected speed/power....found throttle blade screws were longer than they needed to be, which restricted airflow. I mean the screw was so long that the threads were nearly touching the bore of the carb at wide open throttle. I ground the biggest part of the threads off, not so much as to make the screw able to come out, but took a good bit off. Guy called me and said it was a LOT better (in his words). Worth looking at. Also you can look at the transition between carb intake to the carb and then from the carb to the intake manifold. If there is a mismatch (and there usually is) in size, you can carefully grind the surfaces until they are all the same size. I just normally look up in the carb with a flashlight and usually can see a big mismatch if there is one. Some of them are perfect. It's fine for the carb to be a little smaller than the intake manifold bore but if the bore is smaller than the carb, open it up. Worth a little bit. Keep the shavings out of the motor obviously. Also if there are any big bumps in the intake manifold or the cylinder head ports, you can clean them up a little but don't get too carried away...you can ruin a head pretty quickly. Just smoothing them is all you want. You don't want a polished port, either. 80 grit sanding roll is fine, and leave it at that.

I was able to see 35 mph and change after doing all the mods. Methanol, etc. I do not use a jack plate and for a really stupid reason. It won't fit in the garage with a JP on it. Without one I have less than 1/4" between the tongue and the overhead door when it's down. clamped to the transom, raised about 2" up. Friend of mine has the exact same boat, but with a 50hp motor, and he sees 36 mph max (typically 35-ish). He ended up selling his. And I put mine back to bone stock configuration, gas, factory intake, factory carb, etc. Back to 28.8-29.6 depending on weather. But more importantly it's reliable, starts great, and is plenty to pull me and my girlfriend around on the rivers and lakes that we frequent. I did no hull mods other than partially removing the weld bead on the back, as running a straightedge on mine, it looked really good. I guess mine was made on Wednesday.

Just a couple thoughts, for what they're worth. If any of ya think of anything that can improve my suggestions, I'm open...them are just a few things I found that worked on mine and friend's stuff.


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## bptjr (Dec 17, 2014)

To turbotodd. Wow! You sound crazier than me. I had thout about a velocity stack like i ues to us on a drag boke. Also while checking throttle plate opening i noticed that the insulator block (between carb&intake) is major restriction.the hole about 1/3rd blocked off. The restriction is beveled directional like its purpose might be to direct flow to each port?? Or 
posslbly to increase velocity?? Any thoughts? I thought of going ahead & port matching just to see, but was a little reluctant because of thoughts of if it was to direct flow would it starve one cyl. Guess thats a just try & see kind of thing.


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## bptjr (Jan 10, 2015)

Finally made it! ! Hit 20.2 @ 5680 rpm. I made my own velocity stack and adaptor plates. I think part of todays gain was due to 41 ari temp. & dewpoint 7 and my home made velocity stack. I am now a happy camper! Special thanks to pappy and turbotodd for good sound advice. Bptjr.


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## DaleH (Jan 10, 2015)

Pappy said:


> The sanded finish builds up a tiny boundary later of *water* over the boats running surface that the passing water travels over and past with less friction.


Error ... it builds up a tiny layer of AIR that cuts the surface tension of the water, which results in less friction.


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## earl60446 (Jan 11, 2015)

Heck, if you can get 20.2 mph, then 21 mph should be easily attainable with a bit more effort.
Tim


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## Pappy (Jan 11, 2015)

DaleH said:


> Pappy said:
> 
> 
> > The sanded finish builds up a tiny boundary later of *water* over the boats running surface that the passing water travels over and past with less friction.
> ...



Not an error.
Laminar flow works the same no matter whether it pertains to fluid or air. 
Break the surface tension by inducing a small turbulent boundary layer and the coefficient of drag or Reynolds factor will be reduced.
The degree I earned in Aeronautical Sciences has served me well in hydrodynamics during my career. Better bone up if you want to continue this!


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## Boat2fast (Jan 11, 2015)

Congratulations on reaching your goal. 

I don't know your exact model. I looked at the 2004 Hondas. In 2004 the 9.9hp engine shares most of its parts with the 8hp model. (Block, crank, pistons)
The Evinrude/Johnson 2stroke 9.9hp shares most parts with the 15hp versions. This makes it possible to wake-'em-up using factory 15hp parts.
The 9.9hp Honda is already the 'hot' version. There may not be too much left to find easily.
With Mercury, the 6-15hp 2stroke are all built on the same chassis, however, the 15hp has its own powerhead. It has more cubic inches than the 6-9.9hp powerheads.

It would appear to the casual observer that OMC may have done this intentionally so as to rule the countless 10hp restricted fishing lakes. If you had the fastest 10hp boat on the lake, chances were good it had an OMC. Still true today.


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## bptjr (Jan 12, 2015)

I wish my 2009 9.9 WAS based on a 15 , but like you said it is sister to the 8. Now i am trying to fab a shorter velocity stack with larger bell. Still experimenting with length & diameter. I also now am studying effects of air&water temp. And humidity& dewpoint. Its amazing how much weather efects rpm. Also thinking about Wetlander coating on the bottom. Anyone tried this? I hear it is really slick.


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