Scrubbing the bottom of UL1 hull?

[kwizz]

I've read in the instructions about taking the shine out of the underside of the hull to release surface tension. Do you just do the sponson area or the entire hull?

Has anyone got pictures of this please?

Thx

[G-UNIT]

I believe its just the sponsons, the bottom of the boat hardley has any contact.
I'm going to try this myself once I get a good base line run in, I ran my boat yesterday but conditions were way to choppy, even for my bj, could'ent even give it full throttle with out blow overs, but the BJ looked so cool catching air.

[kwizz]

I was seriously cut between three boats UL1, BJ26 and Arpro. The BJ looks such an awesome machine for cutting thro the chop. On ly reason I didn't go BJ was thro lack of knowledge of upgrading the machine to UL1 standard.
Love those narrow tall cat hulls!!!!

[kwizz]

So what would happen if you scrubbed the whole underside of the hull would it effect it anymore then just the sponsons?

[m4a1usr]

So what would happen if you scrubbed the whole underside of the hull would it effect it anymore then just the sponsons?

Nope. When on plane only the ends of sponsons and the driveline are supposed to be in water. Scuffing the bottom of a properly setup hydro is not so critical. Just look at what the real hydros use. If its out of the water when at speed then it becomes aerodynamic effects, not hydrodynamic. Scuffing does nothing for aerodynamics.

John

[G-UNIT]

The BJ was my first boat and I learned alot about fe boats from this one, there are alot of mods you can do, like scuffing the bottom, shortening the stuffing tube for more adjustment,
but with the UL-1 not much is needed except a prop change, strut adjustment, air dam if needed and shortening the stuffing tube if needed, love the UL-1, fun boat out of the box.

[kwizz]

Added an air dam last night and scuffed the sponsons, took it for a test this afternoon, OMG it was amazing!
The waters in this area are never smooth, always a little chop. On the few runs i've had with boat it's bucked around a bit, yesterday I added a lead weight to the nose which helped but not like this air dam. I had the boat flat out in both directions with just the dam fitted it was so fast and stable!
Looking forward to getting a 40x57 balanced prop next.

Thanks for the help guys.

[FEJohn]

What do you use to scuff the hull with and how much should you take off?

[martin]

What do you use to scuff the hull with and how much should you take off?

Use 600 wet & dry in linear strokes ( front to back in straight strokes), You only need to do it fairly lightly to just take of the shine of the surface which leaves the very fine scratches. Thanks Martin.

[martin]

Buy the way only do the running surfaces that are in the water at high speed, Dont do the entire under side of the hull. Thanks Martin.

[dreamland s4]

Added an air dam last night and scuffed the sponsons, took it for a test this afternoon, OMG it was amazing!
The waters in this area are never smooth, always a little chop. On the few runs i've had with boat it's bucked around a bit, yesterday I added a lead weight to the nose which helped but not like this air dam. I had the boat flat out in both directions with just the dam fitted it was so fast and stable!
Looking forward to getting a 40x57 balanced prop next.

Thanks for the help guys.

wouldnt air dams cause drag? just wondering because im thinking of getting one.

[martin]

wouldnt air dams cause drag? just wondering because im thinking of getting one.

The very small amount of drag youd be talking about is far out weighed by the hulls capability of travelling a lot faster before lifting, Thats of course that you have the power to go faster either in motor or props. But it will still also run better even at slightly lower speeds if its breezy. But its not going to turn a 45mph boat in a 60mph just by adding a dam. Thanks Martin.

[Fluid]

The important thing when sanding the ride surfaces of a hydro is to get them flat and smooth. You can't do that with 600 grit paper, you need to start with 220 or 320 and wet sand the surface flat and smooth, without any low spots. You will probably go through the paint, so what. This will also help to sharpen the edges of the ride surfaces, very important to low drag. Once the surfaces are flat and smooth, finish with either 400 or 600, makes no difference.

An air dam can certainly increase the speed of a hydro or catamaran - by allowing it to stay on the water at higher speeds. If your boat is stable at full throttle a dam will do nothing but add drag. If your boat blows off at 50 mph, adding a dam may allow you to run 60 mph if you have enough power and prop.


.

[FEJohn]

Thanks guys for your answers. A good weekend project!

[pescador]

I finally got around to truing the ride surfaces of my UL-1 and sharpening the edges, I didn't think they were too bad but after my JAE build I figured the edges could be waay sharper.
It took a fair bit of sanding and filler to get them flat and sharp, the rear edge of the front pad was the most work to square up.
Ignore the belly pan work, I was cleaning up a previous little ding.
I had filled the sponsons with pour foam a couple seasons ago so they are pretty solid.
For the paint, Topflite Lustercoat yellow is a pretty close match (it's on the bottom anyway)
We'll see how she runs in the spring.

[Gen]

so MR PESCADOR
whats the deal with this
does this allow less drag and a faster boat
or more stable at speed ,is it work doing for a sport user..

[martin]

Depending how bad the surface is regarding unevenness making it completelly flat is probably going to make the boat run a bit smoother rather than the opposite but you also have to take into account that if your boat runs faster through srubbing it will become more unstable the faster you go as with any hull. The real bonus to scrubbing in this way & the whole point of doing this is to increase speeds. Naturally any boat that runs faster through whatever mods it becomes more unstable the faster you push the hull. The way i see scrubbing the hull is its free speed for very little effort as we spend small fortunes on other mods & upgrades some times for quite small increases in speed. But you really need to have the boat sorted so as your getting close to maximum with your given setup to benifit as its not going to turn a wet running or badly setup boat into a good un. What scrubbing does is with the roughened surface a thin film of water sticks to the hull so you have a water membrain between the hull & the lake water, So you have water sliding over water which has less drag than a nice shinney finish. Old ideas of highly wax polished surfaces having less drag i think have proven not to be the case. A lot probably cant bring them selves to scraching a nice new hull up though. Just my thoughts. Thanks Martin.

[martin]

Another relatively simple mod that works well on hydro or cat hull but not monos is to have a square lower halve to the strut rather than round as most do so the bottom of the stut parallel with the shaft in the strut is flat on the bottom. So its running on this flat surface rather than the traditional half round shape strut bottom. This flat surface gets the prop up to & maintains ride height much better. Ive noticed that a few manufactureres have also started to use the square flat bottom stuts now. You cant use these on monos because of the boat leans over in turns. Thanks Martin.

[pescador]

so MR PESCADOR
whats the deal with this
does this allow less drag and a faster boat
or more stable at speed ,is it work doing for a sport user..

Blueprinting or truing the sponson bottoms should help with speed and stability. Making sure they are not only flat but parallel to each other will make any hydro more stable.
One of the secrets to the Zippkit's JAE is the sharp edges so water shears off instead of curling up the edge and causing more drag.

But when it's all said and done will I notice a difference? I have a radar gun now but I didn't get any numbers before doing the work.

[JPriami]

I'd like to see some up close pics of it done with 600 grit if anyone could, that would be great.
Ive always done it with fine 1000 and in circular motion. Martin mentioned otherwise earlier today to me. So im seeing whats being done here.
Thanks,
Justin

[Grimracer]

Flat bottom struts have been around for many many years.. I dont recommend a flat bottom strut on the UL-1. The flat bottom struts come from just past the old straight shaft days.

Truth is I do all I can to remove lift from the strut and the rudder.

Also.. about a 320Grit is best for scuffing the bottoms. Any smoother then that and you really are not doing to much. Scuffing BTY is different then blue printing but we usually combine the two because we are laying waist to the paint down there anyway.

Good boating all!

Grim

[Gen]

Flat bottom struts have been around for many many years.. I dont recommend a flat bottom strut on the UL-1. The flat bottom struts come from just past the old straight shaft days.

Truth is I do all I can to remove lift from the strut and the rudder.

Also.. about a 320Grit is best for scuffing the bottoms. Any smoother then that and you really are not doing to much. Scuffing BTY is different then blue printing but we usually combine the two because we are laying waist to the paint down there anyway.

Good boating all!

Grim

so grim ,we use 320 paper and liner front to back or round motions ,should we sand right down to get a flat surface on ride pads or is this not really necessary ,??

,also i have asked others but ur the man what is best strut depth for 40/57 prop ? and what bout 40/52 can we be the same i was gonna go 1 1/8 ?? thoughts ..thnx dude . ul1 rox

[Grimracer]

Gen

Sanding the ride surfaces flat to me needs to be done on ALL fiberglass boats. Some people don’t like the idea cuz it messes with the paint.. I say all is well!

After you have them flat go ahead and scuff them with 320. ANY PATTERN will work.. No particular "Secret" to that.. Just scuffed.. If I told you what was used to set the B Sport tunnel record you would not believe me anyway.. I hardly believe it! (I was asked by the people that set the record to zip up on that subject.. so Zipping I will do).

But I can say that scuffing is a great performance step!

I have found that running the strut as low was possible and keep the boat on the water is what I go for..

Here is why:

The aft plane of the UL-1 is set for a strut depth of 3/4”. If you run the strut a bunch deeper then that the boat will start to loose the air too early and the boat will start to porpoise and chine walk. Having said this, I have been able to make the boat run OK at 1” depth but past that and its not as consistent.

For the 40X57 I would stick around an 7/8”.. for the 40X52/3 I would try to tune to that ¾” strut depth.

Happy running!

Grim

Remember, each time you make a strut adjustment you have to re-adjust the turn fin!

[Brushless55]

Flat bottom struts have been around for many many years.. I dont recommend a flat bottom strut on the UL-1. The flat bottom struts come from just past the old straight shaft days.

Truth is I do all I can to remove lift from the strut and the rudder.

Also.. about a 320Grit is best for scuffing the bottoms. Any smoother then that and you really are not doing to much. Scuffing BTY is different then blue printing but we usually combine the two because we are laying waist to the paint down there anyway.

Good boating all!

Grim

How is this done Grim?
my UL-1 by the way

[Gen]

well here is mine done ,( i think ??) do i need to do front ride pads too ? ,

and can you give this a light coat of paint or does it defeat the purpose ?

and mr grim you say you need to readjust the turn fin as well after adjusting strut ,to a guy who knows minimul what do i need to adjust and how and WHY ?

with the turn fin it goes forward and back a bit what does going forward compared to going back do to ride ?

thnx .

[Gen]

anybody ????????


this ul1 forum was pumpin b4 they split it up

[Fluid]

The front sponson surfaces don't need to be scuffed although it would hurt nothing. Leave the sanded pads alone, no paint!

The fin can be a tuning aid. Rotating it forward slightly will help to loosen the boat while rotating it slightly back will help to keep the boat stuck down. Only small changes are needed and the results can be subtle. If you raised the strut, then you will want to rotate the fin back a tiny bit....if you were happy with the way the boat ran before.




.

[longballlumber]

well here is mine done ,( i think ??) do i need to do front ride pads too ?

No your off to a good start working the areas where the boat will ride on; hence ride pads.

and can you give this a light coat of paint or does it defeat the purpose ?

Not necessary

and mr grim you say you need to readjust the turn fin as well after adjusting strut ,to a guy who knows minimul what do i need to adjust and how and WHY ?

This one isn't "easy" to answer because every boat acts differently, every prop acts differently on a boat, and every strut change makes the boat different... yada yada yada... There are some "rules of thumb" for making prop, strut, and turn fin adjustments and those can be found in the instructions. I think the key here is, it’s not just ONE adjustment that makes your boat faster or handle better. You will need to work the entire set-up to get the most out of any one combination. The best way to do this is test, test, test…. Keep track of your adjustments via a notebook and only one adjustment at a time. Changing props may make the boat faster, but if it’s uncontrollable or running too light what’s the point? Now, if you make adjustments to the strut or fin to make it faster and more stable your making head way with the boat.

with the turn fin it goes forward and back a bit what does going forward compared to going back do to ride ?

This changes where the turn fin is in relation to the CG (Center of Gravity) of the boat. Much like moving batteries front or back. This can affect blowovers and spinouts....

Later,
Mike

[Fluid]

with the turn fin it goes forward and back a bit what does going forward compared to going back do to ride ?

This changes where the turn fin is in relation to the CG (Center of Gravity) of the boat. Much like moving batteries front or back. This can affect blowovers and spinouts....

This simply isn't true with hydros having bent fins. Those tiny changes made by rotating the fin would make no difference in the relative CG position. What DOES make a difference is the change in the angle of attack of the bends in the turn fin when you rotate it. The bend makes the fin act like an airplane's elevator, lifting or submerging the right sponson. This is what changes the ride attitude of any hydro running a bent turn fin. Rotate the fin 30 degrees forward or back and see what happens....




.

[longballlumber]

This simply isn't true with hydros having bent fins. Those tiny changes made by rotating the fin would make no difference in the relative CG position. What DOES make a difference is the change in the angle of attack of the bends in the turn fin when you rotate it. The bend makes the fin act like an airplane's elevator, lifting or submerging the right sponson. This is what changes the ride attitude of any hydro running a bent turn fin. Rotate the fin 30 degrees forward or back and see what happens....




.

Jay, I agree with 100% with your post... However, you used one key word he didn't in the OP's question: ROTATE.... I should have assumed he was talking about the rotation of the fin, not the fore/aft movement of the turn fin.

Later,
Mike