Purchased an 89 XTB-21--Looking for prop & prop to pad advice

[FastCat04]

Just purchased a 1989 Allison XTB-21 with a 2000 ProMax 225 on it. Love the boat !!!! Prior owner replaced the original sportmaster LU with a standard LU. Also has an over the hub style prop. (I'll try to post pics below).

I do know the standard LU's don't like speeds past mid 70's or so, and I'm not looking to run 80+...but it's a bit of a handful due to chine walking bad when getting the nose up above 'flat'. About 70 is about where it starts to get sketchy. Now I own and have owned lots of BassCat's and can comfortably run my Eyra at 80mph. So I'm thinking I probably have several other issues that I'm looking for advice on please.

1) Boat has a manual jack plate ( cable/ratchet ) and the plate is all the way down....but the engine is mounted all the way up on the plate ( C-hooks on clamps are 4" + above the mounting plate). Probably not the best set-up ?

2) What are some rough #'s that this model boat likes for prop to pad measurement? I haven't checked mine yet....but I think it's probably way out of spec with the set up I purchased it in.

3) Thoughts on this over hub style prop on a standard LU? I'm thinking about swapping to one of my Fury's.

Thanks in advance for any input !

IMG_3820.jpgIMG_3832.jpg

[1Holeshot]

I would go back with a Sportmaster LU or have a Bob's low water pickup nose cone added then start working on setup.

[allisonjr]

I run a sportmaster gearcase with 1.87 gears. I run an SRX 27pitch prop. Loaded down i still get 86mph out of it.

[1Holeshot]

If OP decides to cone the lower unit on the engine need to have a heavy duty bearing carrier installed. Running a surfacing prop on those units will cause prop shaft bearing assembly to " chatter out" the very fine threads in the lower unit.

The Sportmaster LU can handle the extra engine height and surfacing props.

[Hammmerhead]

That thing will be fine in the lower 80's even with the TM unit. I would start 2-3 inches below the pad and slowly go up from there and watch you water pressure. I would try both style props and get a feel for what it likes. That Promax needs to rev, so dont kill the powerband over propping it.

BTW, youre going to have to drive it. The deadrise on that hull is twice as steep as any BassCat hull.

[wbh1954]

.. You need a Low Water Lower.. Put the Center of the Cone Even with Bottom of The Pad.. Mine is 12" Back. I got a 29 & 28 SRX. Worked by Billy Eaves for XTB. Several 4 Blade Over Hub worked by Billy also.. You got go out there & Drive it..

[revlimiter]

If OP decides to cone the lower unit on the engine need to have a heavy duty bearing carrier installed. Running a surfacing prop on those units will cause prop shaft bearing assembly to " chatter out" the very fine threads in the lower unit.

The Sportmaster LU can handle the extra engine height and surfacing props.

How does the different carrier have any effect on the carrier nut? I agree a hd carrier is nice but certainly not required.

[revlimiter]

Just purchased a 1989 Allison XTB-21 with a 2000 ProMax 225 on it. Love the boat !!!! Prior owner replaced the original sportmaster LU with a standard LU. Also has an over the hub style prop. (I'll try to post pics below).

I do know the standard LU's don't like speeds past mid 70's or so, and I'm not looking to run 80+...but it's a bit of a handful due to chine walking bad when getting the nose up above 'flat'. About 70 is about where it starts to get sketchy. Now I own and have owned lots of BassCat's and can comfortably run my Eyra at 80mph. So I'm thinking I probably have several other issues that I'm looking for advice on please.

1) Boat has a manual jack plate ( cable/ratchet ) and the plate is all the way down....but the engine is mounted all the way up on the plate ( C-hooks on clamps are 4" + above the mounting plate). Probably not the best set-up ?

2) What are some rough #'s that this model boat likes for prop to pad measurement? I haven't checked mine yet....but I think it's probably way out of spec with the set up I purchased it in.

3) Thoughts on this over hub style prop on a standard LU? I'm thinking about swapping to one of my Fury's.

Thanks in advance for any input !

IMG_3820.jpgIMG_3832.jpg

With a stock carrier start a few inches below and watch your water pressure as you come up. A 26 trophy is a nice all around prop, promax and pro et props run great also. As mentioned, to get the full benefit you'll want a coned case or a sportmaster. With those you'll start at 1/4 below to even then adjust from there. Engine height is a reference more than anything, you can set it up 3 different times and have 3 different people measure and you'll come up with 7 different answers, haha. Always measure to center of propshaft, not the cone because the point of the cone is not necessarily the same as the propshaft. As far as the other props, try anything you can get your hands on, you'll never know what runs well!

[1Holeshot]

How does the different carrier have any effect on the carrier nut? I agree a hd carrier is nice but certainly not required.

I read my post again and failed to see any mention of prop nut.

If you are running a surfacing prop above pad the top blade will come out of water as it rotates and “ slap” water as it submerges again placing sever stress on prop shaft which is supported by bearing carrier.

If you think the HD carrier is not needed then run what you want but you will save having to buy a new LU housing when your bearing carrier “ chatters” stripping the fine threads in your lower unit.

[revlimiter]

How does it matter which carrier the nut has squeezed in there? The nut and threads see no difference.

[1Holeshot]

How does it matter which carrier the nut has squeezed in there? The nut and threads see no difference.

The nut is not the problem. The nut holds the prop on the prop shaft which is held in place by the bearing carrier. The bearing carrier is threaded into the very fine threads just inside the lower unit housing. A stock bearing carrier does not offer as much support within the housing as a heavy duty bearing carrier. The lateral thrust of a surfacing prop cause the threads inside the housing to strip out over time.

If you are unable to comprehend this explanation then I have no more information for you.

[revlimiter]

Haha, I am not talking about the prop nut, I'm talking about the bearing carrier retainer nut that threads into those fine threads that you're talking about. The carrier does NOT thread into those threads, it slides in and is held in by the retainer nut that's torqued to 200+ ft-lbs. Don't matter if it's a hd carrier or stock carrier, stock type gearcases/cle/sportmasters all use the same threads on the inside of the case and same retainer nut to hold the carrier in.

The only difference in carriers is that the HD carrier is more robust and less prone to breaking due to the stresses you speak of, nothing to do at all with the threads. I've put a lot of miles on a lot of coned cases with no issues on stock carriers, running at even or above the pad. I'm not arguing a HD carrier isn't a nice idea, but certainly not required for the issues of stripping threads like you say.

All that being said, I do prefer a sportmaster just due to the robustness and no epoxy to come off and just a lower maintenance unit on a surfacing setup.

[silverbullet02]

Haha, I am not talking about the prop nut, I'm talking about the bearing carrier retainer nut that threads into those fine threads that you're talking about. The carrier does NOT thread into those threads, it slides in and is held in by the retainer nut that's torqued to 200+ ft-lbs. Don't matter if it's a hd carrier or stock carrier, stock type gearcases/cle/sportmasters all use the same threads on the inside of the case and same retainer nut to hold the carrier in.

The only difference in carriers is that the HD carrier is more robust and less prone to breaking due to the stresses you speak of, nothing to do at all with the threads. I've put a lot of miles on a lot of coned cases with no issues on stock carriers, running at even or above the pad. I'm not arguing a HD carrier isn't a nice idea, but certainly not required for the issues of stripping threads like you say.

All that being said, I do prefer a sportmaster just due to the robustness and no epoxy to come off and just a lower maintenance unit on a surfacing setup.

+1

[1Holeshot]

Well I guess some good came from these exchanges. We both agree a Sportmaster is a better choice and is more robust.

[wbh1954]

I been running a Allison sense 1975.. Tower Of Power. Right up to the 2.5.. Never lost a Carrier. Never.. PM. I have Run the Hound out of all of them..

[FastCat04]

Thank you all for your input ! Will make changes this weekend and provide results ! Once again....much appreciated !!!!