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W. Tripp

Hull Balance

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With all of the recent discussion on hull balance, let's start a seperate discussion on this much needed topic.

My .02:

The balance of the hull both front/rear and left/right seriously changes the handling charicteristics of the hull. The weight of the engine and midsection, the amount of set back, the location of the fuel tank, batteries, trim pump, etc. all affect the balance of the boat. The balance point for a light lay up hull and a standard lay up can very easily be different.

The balance point front to rear will affect how well the boat launches and then lifts from the water as it gains speed. If it is too far back, the boat will launch with a bow high attitude and will be very trim sensitive at speed. Too far forward and the boat will have problems lifting from the water and can easily have problems hooking up the prop and feel "loose" at speed.

Right/left balance affects the angle of the pad and if incorrect at speed will allow water pressure to roll off the pad at an angle losing lift and efficiency even to the point of dragging a sponson in the water at speed.

Gearcase type can change the amount of lift and drag at the most rearward end of the lever. A stock Sportmaster tends to have a lot of tail lift that can change the way the boat handles and the balance point may need to be altered. Modifying the case for less tail lift is a better option. The location of a nose cone mounted on a gearcase can add or decrease the lift of the case at speed by changing the cone's centerline compared to the centerline of the prop shaft. A SSM has less lift, but the props tend to have quite a bit.(Others should feel free to add more on this).

The tail lift of the prop can change the forces acting on the boat. Rake angle, blade design, tip cup, and trailing edge cup can all change the way the prop lifts the boat and acts on the balance of the hull.

Propshaft height can change the way the boat rolls left and right due to the force of the prop and the lift of the gear case. On a right hand rotation case, too low shaft height, and the boat can have a tendancy to roll left. If it is too high it can tend to roll to the right. Way to high, and the prop can blow out at speed.

Time for someone else to add their input and/or challenge this info. Dixon, Randy, Anthony, RBT......anyone?

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Great start Wayne!.

Anthony added a post on the "Do STV's blow over" thread, and I was going to answer his questions there, but decided this dedicated "balanace" thread is a better place.

While Anthony made the comment about STV's being easy to setup, there is some truth to that, but there are an awful lot of slow STV's out there. If you have a 2.5 and cant go 110 in a Euro or closer to 120 in a rocket you are missing the boat so to speak.

Placing the rigging where it was intended originally is ok, it is ok for a stock weight boat with stock power, but once you alter the weights that balance is thrown way off.

For instance a STV that has a midrance hop... is off. None of mine had the hop, Snowmans, AlexR, PaulB, Blake and any others that I run with regularily are effortless to run. There Balance is in the motor height, setback, driver weight, batery placement, pump placement and prop. The exception to the above is Blake and the Barney boat, it has a lot or weight shifting done in it, but it is a 510 lb hull. The weight in it is half way between the driver and the tansom, and has 20lbs of weight added to the front bulkhead. I will add pictures.

The last Mod-vp boat I did ( it was a the rumble and people that were there can attest to how fast is was ) has all the weight right behind the driver.

For the boats that run outside the box, std rigging isn't even close!

RT

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Wayne,

As always very well said. You have covered about everything. The only thing I could add would be this: One of the most common things I see effect the "balance" is the nut behind the wheel. More often than not some pilots try to "drive" the boat and end up overdriving it. They don't let the boat take a set or mess with the set up so much that the boat performs sub-standard compared to it's potential. I sometimes have to tell guys to back up a bit, be patient, and only try ONE thing at a time not four things. Once back on track the results usually follow.

Randy

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YEP...you guys got it covered...THANKS to all.

I actually am very impressed at the balance of the GPI RR and the one Micheal ran...when you see an stv sponson right out of the water that makes the sponson look like its been lowered really is a testament to how well your boats are balanced....well done guys..

I can add on the gearcase stuff a bit if you watch this video

http://www.pbcc.ca/video.html

You'll see that my old stv pcs with the Bob's drive ran too bow high even with a low rake merc cleaver. It was truly the wrong case...bear in mind that some speeds are slower in the video and you can tell we are not over the hump yet, very bow high, however some of the higher speed stuff was just around 100.

So the extra tail lift of the SM really helped this hull go from a 99 mph ride to a 105 with a small 240 hp engine.

Also you will notice the drag of the speedo pitot coming off the hull...that's a lot of water and drag to scrub speed:)

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Good read. Anyone have some insite as to the best place to mount a battery in a Euro? Leave it out in the sponson? My boat always seems to take a better set and run faster and flatter when I have a passenger the same weight as me. (170lbs). Most of my best speeds are with a passenger. Trim pump is at the back on the same side.

Thanks!

post-70-1110903591.jpg

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BRAD,

i think that loaction looks pretty good....I would tend to favour as close to center as possible while obviously offsetting a side steer solo ride.

If and when I ever get a Euro I am considering some up front seating changes for balance. I know the dash may not lend its self well but I would consider changing the seating close to centre line...shoulder to shoulder. The Dash may require some design and you should still be able to access the front seats by walking around the sides of the seats

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Anthony,

that is exactly what I was going to do if I kept my euro. The other idea I was thinking was to put a front bench seat in. Either way the goal was to get me in the middle of the boat when I was solo. I found the same thing as Brad, all my best runs were ALWAYS with a passenger. The dash would have worked.

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Personally, I wouldn't sugest moving the seats together in a Euro. I actually moved the ones in mine as far apart and as far back as possible.

Try putting a 25 pound bag of shot under the front passenger's seat cover to help side to side balance. This worked well up to 130+ mph in mine.

I usually carried a small cooler in the side pocket on the passender's side and didn't need the weight under the seat for runs up and down the lake.

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Still one of the nicest Euros' on the eye...Thanks Wayne

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That was a pretty Euro Wayne, and to think how SPECIAL it was, I highly doubt there has been another like it, and no question none have a bottom like it. It is the only 130 plus Euro I know of.

RT

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Wayne where was your battery?

I could ask Terry, one of the previous owners, but he probably forgot already. I believe your boat is now in the Chicago area.

RP suggested I add some shot where you had it as well.

B-RAD

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My battery was in the same location as yours, but a few inches farther back. The trim pump was mounted to the knee on the other side of the fuel tank. When I raced it, I used a much larger group battery, and the Odessey battery for 24v trim was on the same side as the trim pump.

I built an aluminum box to hold the extra weight for racing, that mounted under the rear seat right in front of the fuel tank. I weigh 205 to 210 pounds and I used 15-25 pounds under the passenger seat cover to counter my weight.

For racing I also had a feeder fuel pump and a vapor tank feeding the Weldon 2015 fuel pump all mounted behind the fuel tank.

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Thanks Wayne, sounds like a nice set up.

Just to clarify, I pulled my battery out of the sponson. You can see where it was. The battery hold down is just sitting where I was thinking about putting it. I was actually thinking more to the front. Maybe I'll put it on slide brackets with perforated holes so I can slide it back and forth. Wouldn't be hard.

B-RAD

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The STV's seem to like weight right in front of the tank, but in the Euro, too much weight this far forward is difficult to get to lift from the water when you have two in the fron seats. By myself, the batteries wanted to be mounted near the front of the tank for best handling. But with two adult males in the front seats, it seemed to like the weight mounted more rearward.

This was in my Euro that was a Double Kevlar and Okume lay up.

Yours might want it in a slightly different place. Test with the prop and weight you usually have in the boat - this will make you happiest with the boat. Don't set up the boat for speed runs with the boat stripped of all weight if you will only run it like this a few times a year.

Also do yourself a FAVOR. Put an inflated inner tube under the front deck. This will keep the boat from sinking like a rock should the boat ever get filled with water or wind up wet side up.

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Also do yourself a FAVOR. Put an inflated inner tube under the front deck. This will keep the boat from sinking like a rock should the boat ever get filled with water or wind up wet side up.

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For some guys that inflatable thing in the bow would be thier girlfriend... biggrin.gif

sorry I couldn't resist ph34r.gif

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The inner tube will fit through the speaker holes in the bulkhead.

I tried it with the rear seats removed, and with a tonneau over the back. It was slower, and drove "squirlly" either way. Both ways seem to screw up the airflow over the open cockpit by moving the decks aero lift to the wrong place.

The top deck of the euro has more of a wedge shape than the RR of ModVP decks. It does strange things to the drag and lift of the Euro. You ought to see the low pressure area behind the rear seats lift a tonneau. Just tape a plastic tarp or drop cloth over the rear portion covering the inside to see what I mean.

Anthony - that was GOOD. LMFAO

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Damn good reading guys.One question.Can there be a happy medium for balance front to rear for a guy like me who wants to drag race and run some top end and get the most bang for the buck so to speak balance wise.I know engine hight would be adjusted accordingly but can ya SET IT AND FORGET IT for a guy like me who wants a little bit of it all?? biggrin.gif

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I will be willing to bet that whoever has my Euro will find a very nice innertube and nylon cover up under the deck that I put there years ago.

My new yellow River Rocket will get the inner tube treatment as soon as the I get a chance - I can't believe that it has take me this long to get it done, but I only have 4 hours on the engine so far - all break-in time.

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HOT SHOT-

A good rule of thumb is to balance a RR and a Euro front/rear right at the front of the fuel tank. Weight here seems to be carried very well. That is more than likely why the rear seats are located at this point.

This is just a rule of thumb.

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I know the Lightning may be diffrent than the Triad but in this pic you can see that the fuel tank is as far forward as it can go unless it's moved to in front of the rear bulkhead.Wouldnt that be too drastic of a change?user posted image

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