OB Skater CG Discussions
 

Thought I would start a new thread rather than hijack someone else's. Here is some video footage of the x cats running with 400r's.
The Austrailan boat has it right. If the video does not play I had to tape the blank box and it appeared.




https://www.facebook.com/nonsolomare...7962075004233/

Nice Video Ron, Guess all that extra weight doesn't matter that much there. They seemed to have balanced their rigs pretty nicely. Wonder if they have any balast added to the front end.

If you look close most of the boats have filled in the notch in the back, so they run better in the rough.

The Gold Coast boat looks a bit bigger?

They all sounded pretty good though. :D

Gold Coast is a Doug Wright so it should be the 32.

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Photo Credit: xcatracing.com

http://i1238.photobucket.com/albums/...ictoryTeam.jpg

Doug Wright actually asked Gold Coast how they balanced the boat with the additional weight of the 400Rs. They replied it was balancing well and that no additional ballast in the front was needed for flat conditions. So does this imply that they have ballast up front and didn't have to add to it or that they have none and didn't need to put some in?

Changing the rig from 2.5L to the 400's is a major shift to the rear in CG.

When Bam had Ron/TNT Marine redo his 28' SKATER with the XS' the CG shifted. JT's fix was to drop off 2x 80lb sacks of concrete (1 at the front of each sponson). We all know JT is a bit of a magician on throttles but his exerience setting up a boat is to notch and would have known how much that amount of weight would influence a pleasure boat and that it was required...

A bare bones race hull would indicate an exact amount of weight has been added or shifted forward within the boat to get them to fly true depending on each teams preference on how to counteract the weight of the 400's.... and a lighter boat is a faster boat when the power is equal on efficient hulls

We may never really know for sure. Most race teams keep their set ups to themselves and not share anything. There was ballast and a ballast tank in the Mobil one boat and no one knew anything. I am sure they did something in the rigging. You cannot hang that kind of weight on the back and not do something.
Regarding the step in the transom the set back acts like a step if the motors were mounted on the back of our skaters with no set backs.

Great thread, Ron! Regarding the transom setback, it is my understanding that steps are there to aerate the hull to release it from the water. If so, what is the effect of the setback? It appears that it allows water to rise behind it which effectively puts more of the gear case bullet into the water stream?? and give more leverage to the force of the prop??? As you recommended, hopefully soon I will start testing CG changes on my Skater. I was more than impressed with the attitude of the X-Cats!

Like Speicher said: "A lighter boat is a faster boat". Racers hate to make their boats any heavier than they are. If anything, I would think they shifted some static weight around to compensate. It does seem like they have a nice set so far.

I have some decent size batteries...moving them forward would be a way to change my cg... is that what you and skate did in your 28 and his 308 ron?

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Like this!
Also the 0 AWG battery cable add a chunk of weight. We went with two hots one from each motor and one common ground shared.

Or you could move your Yeti full of Ultra under your feet!

what about set back of the transom? I know steve as mentioned possibly adding it on his 318...if I'd go with 400R's is it needed and if so what about he notch?

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Trim and hydraulic Jackplate pumps on center bulkhead.

All per Sir Ron's expert instruction.

Steve's knotch was filled in because the boat was originally built for ASD7's not because it was getting 400Rs. I believe the current 318 build has a 5" notch. Maybe Seve knows as he has really investigated this matter.

Right now I'm planning on manual Jack plates with standard set back when I convert.

Ron do you know what TNT used on the 308 they have?

Sam, I like the sound of "when I convert"! Hope that you are talking about new engines, though!! :bananalove:

My guess on the notch fill with the Xcats was just to give the hull more displacement to support the extra weight when static.

Has anyone compared lap times in XCat 400s vs the old 280s. There is not a great difference. Keep your eyes out for 3.2 opti's on 2.5 mids at Cocoa Beach.

Could you elaborate please??!!

And aren't the 2.5 lowers time bombs...

Much more set up and run time experience with the 280s, so for the 400Rs to be even right out of the box says something at least.

They will have 3.2 lowers:)

I believe this is referring to the adapter plate Scott Porta is making to put a 300 on the 2.5 mids.

Bill is using Hydraulic Jack Plates from I believe CNC?
Shawn T and the guys are selling the set backs being used on the exacts as well. I think they are being made in FL. I can find out.
I agree that in the scope of things it is better to get the CG right or as close as possible without adding weight. However a light boat in rough water versus a heavier boat with same set up in rough water the heavier boat will ride better and regarding 28's with smaller props be faster IMO. That is why we used a ballast tank on Mobil one boat. By using a ballast tank it allows you lighten the nose or make it heavier if needed. Once the boat is rigged you cannot change anything. I have also seen a few boats with a rail system to slide the weight back and forth to fine tune it based on conditions of race day.

Regarding 28's other than the Kilo runs the Mobil One team never ran without ballast. Those guys won more races than anyone were always out front. Just ask Gary Ballough LOL.
I have been in a few 388's with ballast tanks also.

I gave TNT Bobs 4" Hydraulic brackets. They look real strong i will let you know. I am going to play with filling in my notch in small amounts at a time. It will be a lot of work but i will let you know what happens. The notch on a 30 is way to big 5" deep and 22" in length. I think a 28 skater is 2.5" deep and 16" length. If you run a 30' hard in ruff water you cant keep the bow down. I have owend 3 differant 28' and they are balanced very well.

This is a dumb question but how do you know you're optimally balanced besides having JT drive it? Living in MN, that could be a problem. LOL.

JT wont be the one to do all the testing I will. You need to test and test again. You have to get a baseline in the calm water and in the ruff water with a good set of props. Then start with level trim and a conservative drive height and then your knowledge and seat time will take over. You will run the boat in all directions and all conditions. Keep a notebook with good notes, I know it sound dumb but i find it really works. CG is a very hard to get right because you can mask it with props,and over or under trim. Years ago when we raced we would hang the boats with one strap and it would balance around the second step ? Today with 400r I have know idea where the CG should be.

balancing with one strap is the only way I ever pictured get a true CG. I talked to tres matin about the balance of my sunsation and he said when he rigged he weighed everything down to the smallest nut and piece of wire to keep the boat balanced latterly...even the weight of the driver and throttle man matter.

I think it's safe to say by Talon 22 with twin's was NOT balanced correctly - LOL.

MDS

Balance point when static is one thing. Then you start getting these rigs running, the aero begins moving things around and everything becomes variable. Cats especially with how they start packing air. How do you decide where the center balance point is?

Very interesting point. I considered adding a plate like a Bennett trim tab to reduce this if needed. You could adjust length and/or depth until it produces then desired results the go with something permanent glassed in.

I always considered length but not depth on it. Are you going to alter one or both factors!

yea lots of variables for sure, but you'd have known point to work from and as you moved things for feel you could go back and check it out the same way...get to see how it changes with what you stated...that would be interesting to see.

Putting it together is where the fun is. :D

When you can run in 2-3's with an occasional 4' at 80mph and not feel the nose lift!!!! LOL
You are 100 percent correct things when dynamic are not quite the same as on a scale. I also have had different props for certain conditions. It all factors into the equation.

What pickup would be good on a 28 to get ballast water? How big a tank? 15 gallons? Mount a 2500 rule inside the tank?

I see the fuel burn as a problem if you want to go long distances.

We are gonna go 180 miles on the dam to dam run (2 miles/gallon = 90 gallons X 8lbs = 720lbs).

That's gonna change almost 800 lbs in the rear over the course of the day.

Would be better to start a little light in the bow or better to end a little light in the stern??

Very interesting.....

The fuel tanks in an outboard Skater are generally OVER the CG. Other that all the weight (of fuel) making the boat sluggish, it really shouldn't effect the CG on your 28, much. I assume you'll do the dam to dam run in the early AM so boat traffic (wakes) shouldn't be an issue. I would not add any weight to the nose for that run.

Brett,
You have already had a taste of how your boat responds to rough water with no ballast. If it were me and this is only my opinion I would put 50 gallons a side in no more, I would remove any access weight you can. anchors, additional oil etc. I would 100 percent run the ballast up front based on how the boat is rigged and run the 32" pitch props you had. They will allow you to run well over 100mph and carry the weight better than the 34's.
I can tell you with the way your boat is rigged the ballast will provide far more benefits than not having it. Unless you are the only boat on the lake that day out front you will be good to go.

Just my .02 cents.

Good plan..

That's what we will do.

Now if you guys could all show up and swat away those damn PWCs we will have a clean run :eating:

How accurate or not at all would one be with taking a side profile picture of a boat parked in calm water and having someone with knowledge look at it? Could you tell by the water line?

MDS