I need your help solving a mystery.

There's a 1986 Excaliburcat for sale that has had two interested buyers call me because they found out from the board I own the same model. The boat has had a lot of rerigging. looks good, and the price is a steal, except for one small detail...it's about 10 mph slow. Yeah, I know, they're all slower than the salesman said, but the salesman says this one goes 68 mph @ 4800 with 26 Hydromotive four blades behind new 502 MPIs and Speedy #3s.

You can see from the attached picture that the drives are not Speedys, they are TRS with the lower cases painted gray. Large bullet and thru hub props give that away. So this boat is very similar to mine. It's the same hull, same drives, same props, same prop rotation. The engine location and drive height appear to be the same too. Don't know about the weight.

The first thing the callers want to know is how fast is my boat, and the answer is 84 mph @ 5000 with 27 Hydromotive four blades. I figure my engines have about 460 prop HP, and the 502 MPIs will have about 400 after the trans and TRS, so that explains 6 mph at most. Where's the other 10 mph?

The boat appears to have spacers in the drives. Before I took my spacers out I was going 80 mph @ 4800 with 27 Mirage plus. Before I put in the 500 HP 502s I was running 75 @ 5000 with 25 Mirage using tired 420s which would have less power than 502 MPIs. My speedo reads the same as radar. No matter how I look at it I can't account for the difference in speed.

I would like to help the second caller, a fellow Canadian, get into a good old cat, but he will be disappointed if it's a pig. Any suggestions of where the speed has gone? Is the boat worth looking at or should I tell him to steer clear?

Tomcat.....I'm stretching out on this one but, is there any difference because these are FWC 502's with any extra weight and/or the power output. (along with possible drag from the spacer effect) ??

Bob

Try reversing the prop rotation. I had a chris cat that ran 15-20 mph faster with the props turning in. Depending on the location of the drive (right to left, and its height), the cleaner water may be towards the tunnel. By turning the props in, it lifted the back end A LOT!. Then the air carried the front end. BTW this also allowed for a higher X dimension, gaining a few more mph.
Gary

OOPS, sorry. I was just looking at the pic again. I can't tell from this crappy monitor which way they are currently turning. Looks like they might be turning in. Anyway, they could still try changing the rotation. Especially if the drives are to the outside.
But I would also think that's a little slow. The slippage is a pretty high for a cat. Do you have any indication of the running attitude, ie. bow heavy?
Gary

Hey Bob - I saw your boat on reader's rides, Looks great, just like mine.

I wonder about the power of the engines too. Maybe I'm paranoid but if they were actually 7.4 - 310 HP, with 502 stickers, the speed would make sense. When Mercury came out with the EFI intake they used it on all big blocks for a year or so before the 7.4 got its own intake. I will have to tell my friend to check for the 8.2L mark on the side of the blocks.

Gary - The props are turning in now. I have tried both ways when I had my spacers in and it didn't make much difference. By the way, at what speed did the Chris Cat carry the bow with air?

Excaliburcats tend to be bow heavy to begin with, that's why the gas tank is between the engines. I have told my friend to pay attention to the boat's attitude, trimability, blowout etc. during sea trial, but he doesn't have anything to compare with. I know when the kids climb up inside the sponsons on my boat it runs like a pig, hunting and plowing. It's even worse if they do that now with the spacers out. I don't know how much it reduces top speed, because I tell them to get the hell out of there before we throttle up.

Could a hull soak up enough water to lose this much speed? I keep mine in the water all summer, and have never noticed more than a mile or two difference from that first brisk blast in spring. This is probably due to air temperature more than anything else. Is there a reliable moisture meter that my friend can use to test the hull? I have told him to weigh the boat and if possible lift it off the blocks slightly with one sling to find the centre of gravity. Not that I know where the CG should be, I've never tested mine. Have you Bob?

Thanks for the advice. What my friend really needs is to invite a couple of us old cat guys down to Florida for a test drive, all expenses paid!

With my props turning out, it would dig the ass end in too deep and ride heavy on one side or the other up until 60mph+. When I turned them in, the whole boat felt like it was riding 1 ft higher out of the water, popped on plane much faster, and the bow would easily carry itself at 50mph. It actually felt a little too light in the mid 90s, but you get used to that.
Good point on the 7.4 vs 8.2. I saw a boat with SSM IIs on it, but it had SSM V stickers all over the drive. The owner was convinced they were Vs.
Gary

I hear you. The fact that these TRS drives are being advertised as Speedy #3s would go along with 7.4Ls being advertised as 8.2Ls.. In fact they are claiming 500 HP!

Did your Chris Cat have a porpoising zone and how did you handle it? My Excaliburcat loosens up at 50 and feels good at a cruise of 60 @3700, but it never feels or looks like the bow is floating. It runs flat, and trimming out doesn't change it. As you get close to 80, it starts a mild porpoise in calm water. It's still doing it a 84, I haven't got enough power to drive through it.

Another interesting characteristic is the speed doesn't increase as the gas tank empties. Since it is in the back between the engines, I figure that the CG shifts forward and brings the nose down cancelling any speed increase due to lighter weight. The boat also goes almost the same speed whether it's just me or a whole load of passengers.

All this says bow heavy to me so maybe the porpoise is due to the centre of pressure moving back behind the centre of gravity allowing the bow to tip down. If I had more power then maybe I could get enough air under the bow to hold it up and stop the porpoise.

"Hey Honey, we need superchargers to stop that annoying bounce you don't like!"

"Hey Motorhead - Just slow down!"

A friend of Mine and I were talking about this boat before the Miami show and we were going to get together while in Miami at the Show to take a look at it, but it didn't work out. He did stop by to look at it by himself but said that the place would not give him the time of day! To bad he was really interested in it and it sounded like a good deal, but like you said, the speed bothered me, I thought it should run faster also!

I think you guy's are on the right path
I would weigh it also!! Maybe it is waterlogged??
Check the # on the Blocks and Heads to see what they really are!
Walk up and down it pounding on the hull and listen for water or a soft spot.
If all else fails, take it out and run the Heck out of it, maybe you can find the speed!

No porpoising at all. The drive were very high though, propshaft was about 1" above the bottom of the boat with SSM IIIs. Most of the porpoising in V hulls I have seen were cured by raising the X dimension or shifting weight.
As for being light, the bow was OK, it ran flat at high speeds. It was the whole boat that felt like it was very light. I wouldn't want to try to turn it at all at speed. You dont get much bow lift with the drive that high. As a matter of fact, the boat attitude wouldn't change with more trim at high speeds, but the speed came up.
It would loose 6-7mph with the addition of fuel and 3 people.
Gary

Tomcat........Did you take a look at the pictures from traderonline.com (its a florida listing). Those engines sure look "real", and are FWC...(who knows).....Also, I spoke with you back in 99 when I bought my boat, looking for any spare sunpad items. (mine is exactly like it came in 1986 with the kaama/hardin marine engines and surface drives)........that boat in fla was going for the low 30's i thought without a trailer? Either way, the 68mph seems just too darn slow. It would be interesting to see the running attitude when up on plane. Just to see if its only in the water from the mid-step back.


Bob