1973 xk 22 propeller

[41947]

Does anyone know what the original propeller was on the 73 xk 22 with the 320 hp 350 flv engine? The hull card states the prop was 1218-00042. I am having a hard time cross referencing that number. The boat still has the original engine and 270 outdrive. Any help would be greatly appriciated. Thank you.

[tph]

my prop chart for 1971 xk22 with 350flv shows a
14 3/8 X 19 super cup.
tom
vintage marine

[Paul P]

That prop is an amazing indication of power and speed. I am curious of the actual observed speed you have obtained in this boat. If you can, please provide the top speed and equivalent engine rpm. I'll do some math and report back.

Regards,

Paul

[rgmxk22]

The 14"X19" should be correct and original if I go by the info on the hull card for my 1972 XK22. But what I will tell you is on my XK22, I've been happier with a 14"X21" in the same set-up (320hp CC 350FLV with the Volvo 270 drive)

When I bought my XK, the seller told me that he had switched to a 14"X21" and never explained why. So I tracked down a 14"X19" and gave it a shot. Well, the top end was a little better with the 19" prop, but it gave up a lot of low speed handling.

If felt like I had to give the engine a lot more throttle to get the boat to respond, especially when backing up. It felt, like the 19" prop wouldn't dig in very well at low speeds, but the 21" does that much better.

So for handling in docking situations or loading/unloading on a trailer, I went back to the 21" and have more confidence with it. I kept the 19" around in case it want it or ding up the 21".

With the 14"X21", the engine will turn about 4,400rpm and push the boat to the mid 40's depending on how many people are on board.

Ron Michael
1972 CC XK22
Ohio

[Budgiecat2]

I have an XK-19 with the same engine and outdrive set-up. The 14x21 works well - rpm @ 4400 and top speed mid-40s. I also get essentially the same performance out of a 15x19 - maybe a couple mph more top end. I think you are on the right track following rgmxk22's comments. Good luck!

[Paul P]

I started to do the math and the numbers certainly do not work with a direct drive setup. Your transmissions must be 1.5:1 gear reduction. Please confirm.

Many thanks,

Paul

[mfine]

Paul, the XK's have an outdrive with what I would guess is between a 1.5 to 1.65 gear ratio.

[rgmxk22]

Paul P,

mfine is right about the gear ratio. My XK22 with the 270 Volvo drive is set up for a 1.6 to 1 gear ratio in the lower unit of the drive. I'd have to go check my Volvo manuals for the exact ratio, but it is 1.6 and change.

Now where someone might hit a snag is that the 270 drive was available in at least 3 different gear ratios. Since the whole outdrive and lower units are very interchangeable, someone could quite easily end up with the wrong ratio for a V-8 engine.

Such as if a used drive for a 4 or 6 cylinder as hung on the back of a V-8 boat and no one thought about the gearing. That would play hell with your RPMs, speed and prop size. Probably wouldn't happen, but it could. But the original set up should be 1.6 to 1.

Hope this helps with your math.

Ron Michael
72 CC XK22
Ohio

[Paul P]

Thanks Ron,

here is the math on paper and of course what happens when the hull actually gets wet and the prop starts to spin is an entirely different issue!

4400 rpm x 19" pitch = 83,600

4400 rpm at 1.6 gear reduction = 2750 x 19" = 52,250

5280 feet in a mile x 12" = 63,360

Therefore

60 miles per hour is to 63,360 as X is to 52,250 = 49.48 miles per hour. Factor in about a 14% slippage factor = 6.9 miles taken off for slippage reality, providing a speed on paper of 42.58 mph.


Going to the 21' prop, providing that the motor is actually able to spin it at 4400 rpm produces a speed of 54.68 miles per hour, reduced by the slippage factor of 14% or 47.03 miles per hour

I am interested in these numbers because I am pushing a similar 23 hull with inboard power in the similar power range but with more torque. My prop size selections are very similar (up to 23" pitch) but my rpm is not as high. The inefficiency of the inboard application may prove to be slower than the transdrive. Time will tell!

From all I have heard about this hull, I think it would take a lot of power to push it over the 50-mph mark. Certainly possible, but not my intentions.

regards, Paul

[Budgiecat2]

We have an XK-22 in our club that runs about 62 mph, BUT, he has a big block Merc Cruiser @ 600 HP and a Merc outdrive.

For our original power combo, mid 40s seems tops. BTW, I ran a 14x23 for while and liked it, but don't have speeds on it - seems like the rpms were down around 4200.

[Paul P]

John Adams (see link) is using the 23 inboard lancer as the basis for his gentlemen's racer customized boats.

http://www.gentlemenracer.com/our-boats.html

I know for a fact that he was using a 13x13 in a 454 powered boat because I checked the prop when it was out of the water. Subsequent conversations with John indicated the same, perhaps a bit more pitch, running with a 1.0:1 direct drive and hitting mid to upper 40 mph speeds.

In discussing the issues with a naval architect at michigan wheel, and with others, everyone with hands on experience seemed to lean toward the 1.5:1 gear reduction and a larger diameter prop. Benefits would be less impact to a fully loaded boat, easy to get on a plane. People were worried I might not be able "to get enough prop under that boat", my project being a 427 inboard. I may be giving up some speed, but the ease of getting on a plane and the fact that I will be loading the boat with friends from time to time, and I want fast and easy cruising over the long distance lead me to go with the gear reduction rather than direct drive. One guy at ACME props told me that the 23 hull with its weight and deep profile was pretty much on the cusp of being able to go direct drive or gear reduction. CC opted for the gear reduction. John Adams opted for the direct drive. Both seem to work great for the particular application. I figure once out of the hole and at speed, John's boats would have a higher top end than what I will end up with.

Good stuff, thanks for all the comments and data.

Best,

Paul

[mfine]

Paul,

If you like math, try figuring out the horsepower and torque requirements for my 3 stage jet unit and the expected boat speed at different RPM's!

The driver in both applications is required torque verses available torque. In order to spin a larger or higher pitched prop at the same RPM you need more torque. Torque times RPM is power, so if you are running at lower RPM, your engine is producing less power and hurting your speed. That would say you need to choose a prop to get the engine RPM into a higher range. The other issue is the slower spinning prop is more efficient. Using the 1.6 gear reduction to lower the prop RPM's gives the outdrive an advantage over a direct drive inboard because they can both run the engine faster to get more power, and spin the prop slower to waste less of it. Also, with the outdrive the drag from the gear below the transom can be lower, the wetted area is less because the engine is further back (less skin drag due to steeper planing angle) and the prop thrust angle is more efficient. In other words, you will have a harder time getting over 50 mph with the inboard than they will with a outdrive unit.

The only thing you can really do is add the gear reduction as you mentioned.

[Paul P]

I'll contact my speed consultant, Keith Brayer. He learned a bit from dad (Curt) 3-time APBA record holder, lol. Those guys know the black magic that goes way beyond paper desk jockying.

As for the math to calculate the jet boat issues, there is one missing link that is hard to quantify, and that is the "crazy factor" of the owner/driver. How can you put a number on that?

Best,

Paul

[rgmxk22]

This is more for 41947's original question, but
all this talk of props on the XK22 got me wondering. I dug out my copy of the hull card for my XK22 to compare and double check the part number that 41947 posted eariler.

He posted 1218-00042 and I wanted to see if my hull card stated the same number. Well, I was surprised to see 1208-00242 and when I crossed that to a Federal Propeller catalog of CC numbers, my original prop was a 14.37"X21".

This is basically the size that I am running currently, but as I stated in my first post, I was under the impression that my XK22 originally had a 14"X19". So learned something aout my boat's prop because of this discussion. I had just never crossed that number from my hull card. I was going by the info the seller had gave me when I purchased my boat.

It's very possible that CC did use other size props on the later XKs, I can't speak to that. But one thing that makes me wonder a little is that the number 1208-00042 that 41947 posted was not listed in my Federal Props Catalog list of CC outdrive part numbers.

Ron Michael
1972 CC XK22
Ohio

[Paul P]

There are some pretty informed boaters who think CC over-propped their boats to obtain speed ratings and match the competition. In reality, few of us ever run at top speed and I would guess most of the exceptions are the guys with the XK and other smaller fast high powered boats that we would refer to as "speedboats". This is also true because the speedboats get better fuel milage than the bigger boats do too. With cruisers it is pretty rare that anyone would be running at wide open throttle for very long at all, and most of the time it is just to impress the guy standing at the helm next to you who is holding a beer, or perhaps to outrun someone in a newer boat to show him some of that classic CC speed.

In the real world, especially lately with fuel prices so high, the emphaisis is much more to cruising efficiency than top speed. I have swapped a lot of props around on my 20' fiberglass Sea Skiff looking at the GPS speed readings, and a pretty stock 327F will just go so fast. In reverse I have literally NOTHING, the darn boat does not want to back up, and I suspect the 23 Lancer and its identical hulled XK22 are also not too good in the docking categoruy. I have gone with a little less pitch and run a little bigger diameter prop to mlighten the load on the motor, and also get it up on a plane faster. For the XK boats, however, they are all about speed and if I had one I would most likely be making it go as fast as it could.

On my 427 inboard Lancer project I will be paying big time attention to the midrange running performance where I will be spending most of my running time, as it will be covering the same route we take in the Skiff too, but will be loaded up with more people. At 2800 to 3000 rpm I want the boat up on a fast plane and the motor running easily.

Back to the topic however, it is great that you now know the true prop designated for your boat. I would suggest picking up one on ebay and giving it a try. There is a chance that you may actually like the one you have on the boat now better. This conversation has also helped me analyize what the best prop would be for my own project, using the same basic hull shape. I agree the outdrive is always going to be more efficient but on this particular hull the wetted area is much greater than any of the classic inboard Chris Craft boats, because the latter are almost all flat bottomed at the transom. The 23 and XK22 become the faster boat as the water becomes less flat

Regards,

Paul

[rgmxk22]

Well Paul,

As you already, know part of your backing up issue with you Lancer is going to be the curse of having a single screw inboard set up. My brother has a 21' single screw Lyman and there is just one direction that it will not back up like most single screws.

On my XK with the Volvo drive, it's not as bad as you'd think because I can swing the drive around and help move the stern the way I want in reverse. It's a big help when you can use the drive/prop to push or pull the backend towards or away from the dock.

And even though my XK is considered a speedboat, I don't run it flatout very often. Unless you have really flat and sweet water, you're just not going to open up. You'll need to go see a chriopractor after the pounding you'll receive. (That's what I get for being a Lake Erie boater) And as you mentioned, the fuel costs.

Usually, on good water, right around 3,000 to 3,300 rpm, the engine finds its sweet spot and things are humming along nicely. Good ride and speed, not pushing the engine too hard and you're just enjoying the ride. Also, I've been told that even though the old Volvo drive is very dependable, if you want it to live a long and happy life, you don't run it over 4,000 for sustained periods. That way you can keep the money for adult beverages instead of repair bills.

I would suppose that would be about the same in a stock Lancer with the Volvo drive and fairly similar with the straight inboard since the hulls are so close to the XK. But I'm curious to see what your project is going to run with that 427 in her. I hope you post that info when you can.

Ron Michael
CC XK22
Ohio