prep work

[johnsonm50]

I turned the wet side up on my hydro this afternoon to wet sand some touch up varnish I brushed on to avoid having to do the whole thing over till winter. I got to lookin & noticed a couple things.
1, the sponsons dont run exactly the same line as the airtraps, they are both out 1/4" to the outside. Being the same Im guessing this is on purpose. Since its not in the water anyway even if not it probably doesnt matter.
2, I clamped a straightedge onto the skeg upwards to hold a carpenters frame square on the bottom & check for square. It was out an 1/8" towards the outside at its bottom. I read the thread on fins & now since I should fix that Im gonna move it slightly out to port & angle the bottom in Im thinkin 1/8 or 1/16. I was practicing turning Saturday & it didnt seem bad as was but I guess you can get used to it too. However it turns out to turn Ill find out soon enough.
Theres been talk about aqua-dynamics on the bottom, sanding w/400grit, etc., what about the air-ed out surfaces, is a wax coated smoothie the way to go or does that just look 'er

[Dave M]

Some Suggestions

I would not worry about your sponsons.

For your turn fin, why not simply square it to the air traps ? Clamp a long level to it, and shim the bracket until you get the same measurment at for and aft of the level. Measure from the level to the air trap. This is probably more important than locating the fin further out from the chine. A properly shimmed fin will track your boat straight no matter where you place it on the sponson back. If you want to play will camber, have at it. I personally don't like it in the faster classes. The torque an 850CCM engine puts out makes it very difficult at best to adjust while going down the straight. .

I am assuming you run a CSH or something similar. At those speeds, I don't think you will notice a lot of difference in how you finish your bottom. You might find tenths of a mile an hour differences. It is important to make sure it is flat and level at the rear, and forward about 3 feet. If the bottom was intended to have a slight rocker, then leave that in as a lot of other measurments are based off this.

[johnsonm50]

I would not worry about your sponsons.

For your turn fin, why not simply square it to the air traps ? Clamp a long level to it, and shim the bracket until you get the same measurment at for and aft of the level. Measure from the level to the air trap. This is probably more important than locating the fin further out from the chine. A properly shimmed fin will track your boat straight no matter where you place it on the sponson back. If you want to play will camber, have at it. I personally don't like it in the faster classes. The torque an 850CCM engine puts out makes it very difficult at best to adjust while going down the straight. .

I am assuming you run a CSH or something similar. At those speeds, I don't think you will notice a lot of difference in how you finish your bottom. You might find tenths of a mile an hour differences. It is important to make sure it is flat and level at the rear, and forward about 3 feet. If the bottom was intended to have a slight rocker, then leave that in as a lot of other measurments are based off this.

Yes, Its a C-20SSH Thanks Dave.

[snyder]

Don't ever, never wax the bottom of a boat, unless you have a death wish.
Ask Mark Schmerbach.

[johnsonm50]

Don't ever, never wax the bottom of a boat, unless you have a death wish.
Ask Mark Schmerbach.

BT-DT Its what I used to do before I heard & read differently. On a much slower scale, [aluminum fishin boat] it works. Even my go fasts arent that fast tho. Definitely askin about the topside on this. Thanks

[johnsonm50]

Anyway, having heard & not arguing that point.. what did happen that waxing the bottoms dangerous? I just heard it wouldnt work- like a wet plate stuck to a table. Was it an unpredictable release?

[Dave M]

Yes

It was an unpredictable release. I agree, no waxing your bottom. That just sounds wrong...

What usually happens is once the boat get to top speed and is running at optimal angle, so little of the bottom is touching the water that what is left will not stick, and you will usually broach and possibly barrel roll in the striaght away. Remember the torque mentioned, it is a constant pull while going straight, you loosen the boats grip and the natural thing for it to do is torque immediately. You will lose most control of steering at that point. Sometimes you can recover, most of the time you can't.

[johnsonm50]

It was an unpredictable release. I agree, no waxing your bottom. That just sounds wrong...

What usually happens is once the boat get to top speed and is running at optimal angle, so little of the bottom is touching the water that what is left will not stick, and you will usually broach and possibly barrel roll in the striaght away. Remember the torque mentioned, it is a constant pull while going straight, you loosen the boats grip and the natural thing for it to do is torque immediately. You will lose most control of steering at that point. Sometimes you can recover, most of the time you can't.

Right , I mean Wrong. Thanks

[Raymond]

Dave, help me understand this. Are you saying that a hull bottom can be too slippery so as to allow the motors torque to induce a yaw at speed?

I understood wax to be a performance thief due to surface tension issues on the wetted surface. I am now confused but intrigued to understand.

[Team B&H]

Of course boat or boat bottoms may not provide enough traction , if you will, so that the boat will yaw or track to the left. While most of us think that the propeller acts like a simple screw in the water to push the boat forward, from a side view it also looks (and works) like a paddle wheel. The blades do not absolutely move perpendicular to the water but there is more than enough angle to provide some side thrust. With the left hand props universally used in contemporary outboard racing, this side force wants to push the boat to the left as it helps cornering and general race course performance when compared to a right hand version. This effect is generally enhanced when using slower rotating, larger blade area props, ie Stock as contrasted with PRO.

The boat or other features must provide enough friction with the water or some other force(s) to keep the effect of the prop side thrust within a workable range. As boats have become more free from the water, all this has become more important. The less the basic hull is in the water, the less it can resist the side force from the prop. Hydros have gone to narrow, full air traps which also act as fins to resist side forces. Stock runabouts generally don't go fast enough to run into a problem here. There is also plenty you can do with the gearcase to either resist the prop side force or produce a counter side force to balance out the prop side force if the boat itself goes too much to the left. And some drivers are much more adaptable to a boat that tracks slightly left than others.

BTW, it was amusing to watch Schmerbauch wax his boat's bottom at Dayton years ago and then take maybe two laps and come back in and ask how he can get the wax off.

[sam]

Well said Sam

[Raymond]

Thank you for the info: lots to learn and eager to learn it.

Raymond