XTB21 handling question

[Blue Gray in PA]

I have read a lot on this web-site about handling and how motor height and cable steering can affect handling. I have an 1989 XTB with a 1992 150 HP Mariner Mag III that is set about 3 to 3-1/4 inches below the pad which is where it was when I bought it but had been higher at one time according to marks on the factory transom plate (5" setback). I had the prop (26" Laser II) reworked and around 60 MPH (4800 RPM) the front end starts to wander left and right like a chine walk. Is motor height affecting this and should I raise it closer to even with the pad? I have three batteries in the back (two on port and one on starboard) for the trolling motor and starting so I know weight at the back is a factor too. I'm pretty sure the cable steering is tight since I adjusted it according to the Allison book. I tried steering it slightly left as recommended but it didn't change the handling and my buddy wasn't cool with trying any more since we were running out of water. Any more info I need to supply or can someone give me their thoughts on what to check and or change before I tow it to the Rally in a few weeks?

 

[badbait]

Since I don't own a XTB21 I would first lookup what the average setback is of all the XTB21 owners on this board. Which I did and I can tell you this, your to deep I would start at 1/2 below the pad and go up from there. The next thing is setback with your 150. I would start at 13" of setback if you don't have much wieght up front. If you usually have a fishing partner and a heavy trolling motor plus a lot of gear, I would go to 14.5 inches of setback. The way its setup now you would be lucky to run over 60 mph. Hopefully an XTB21 owner with a 150 or 200 on it will chime in here.

 

[RedAllison]

The first thing to ask is do you have a pointed gearcase? I assume not as the motor is so deep. If your case is stock then you wont be able to raise it much over 3-2.5" below pad. Speedwise you dont need a pointed gearcase, but by having one you will be able to raise the propshaft closer to the pad and run surfacing props like ETs, Choppers, Hoss' etc that will maximize yourset and make handling MUCH easier. The only non pointed case I have driven on an Alli was on Jims GS at lastyears rally and too me it felt "heavier" than others that are running freer. If you have to run such low propshaft heights then you might wanna try some Trophy's or Tempests. The Tempest is a fast prop for what it is, especially on a rig like yours!

You might just wanna load up whatever props you got and come on too the Rally. There will be a PLETHORA of smartguys there that will have you maxin your rig out in less than an hour!
RA

 

[froggy]

Blue Gray,

I had a, brand new 1985 XTB 21 with a stock 1985 200HP Merc. I did add a CLE gearcase housing to the motor. My setback was 4" (that's what Darris was recommending at the time). I always ran with a fishing load and two persons (the XTB was real hard to balance with only one person).

My final setup was a Merc Chopper II, 28 pitch prop, modified by Hoss Props. I could turn this prop 6800 rpm with a load (the stock diaphragm fuel pump pooped out at about 6800). My engine height was set at 1" above the pad and my loaded speed was always in the low 80's.

I loaded as much of my stuff in the back as possible and only had rods in the rod box and life jackets/cushions and cold weather stuff forward.

I hope this helps.

froggy

 

[davet553]

I once owned a 1990 xtb21. The best setback for the xtb is 9-10 inches. Mine had a stock 1995 225pm, & would run 91-92 mph @ 3/4" below the pad. Handling was solid,easy one hand driving. As was said before, you do need a nosecone/bottom water pickup, to get optimum performance. Hope this helps, DaveT

 

[Blue Gray in PA]

Thanks for the input guys. I have a stock nose on the lower unit ( no point) and the factory setback of 5 inches. Almost all the weight is at the back except a 21# anchor, an 82# thrust trolling motor and some life jackets. I had the boat to 65 MPH at 6000 RPM last fall (before reworking the prop) and with 1200 RPM to go now, I should be able to get back to the 75 MPH the previous owner achieved I just need the handling to improve to get there. I spoke with Glenn Reynolds previously and he recommended this setup as a good all-around arrangement but the handling seems to have degraded since reworking the prop.

Badbait - where did you find the listing of prop depths and setbacks for XTB21 owners? Is there a section on this site I haven't found yet?

RedAllison - you said I need a pointed case to go higher. I know the current motor is the second one on this boat so perhaps the first one was set higher and that's where the transom plate marks are from. I also wonder about the cable steering getting bound more with a steeper angle. It works OK now but would definitely be more tightly angled if I went higher. Can I try raising the motor or will it handle worse without a pointed nose? Should I try putting more weight forward or will this have no effect?

Dave T - did you buy another jackplate and use the factory transom mounted plate with a longer rear section to achieve the 9 inches? Does the 225 versus the 150 I have make a difference?

 

[badbait]

The first screen that shows when you come to this site has a little red boat with black flames and it's all aired out. Well look to the left on that screen and it lists all the models. Click on XTB and it shows that there are about 25 owner listed there. Most of the owners have there setups posted.

 

[jdm90]

Blue Gray, your not alone. I too am having similar results with a similar setup on my '90 XTB. Motor height is about 2 3/4" below - that's as high as I can get it now without unbolting the motor and remounting - ( which I am itching to do ) and the same setback as yours. I do however have low water pick-up on lower unit. Keep us posted if you have any luck with different props. If someone could tell me the safest way to lift my motor in order to mount in lower mounting holes I am considering raising it.
David

 

[GPI Racing]

Blue Gray in PA,

Bring your boat to the rally. In 20 minutes I'll have you pretty comfortable in your boat. Your set up is not that far off. A little instruction and you'll be just fine. I sold several XTB 21s and most guys need a little guidance. You'll find that your probably "over driving" it and helping the chine walk rather than correcting it. Your 26 laser 2 is a great prop to start with so don't dispair. I have a feeling that I can show you how in a very short time. Your discription is very common and not truely a mechanical problem in set up etc. The offer stands to get you flying level...see you at the rally.

Randy

 

[Blue Gray in PA]

You're on Randy. I will agree that it could be driver error since I have not had it out since last year and got very little high speed seat time then due to small lakes and short river sections prior to the next lock and dam. I will be arriving Tuesday afternoon with the family so feel free to call me at 724-664-6445 anytime after Monday AM and we'll be on the way down. We can definitely set something up for early Wednesday if you have time. Unfortunately I don't have any other props to try but will definitely appreciate any advice.

JDM90 - I was told my a local shop (I've heard they are competent) that you can stand your motor on the skeg (get it straight vertical first of course) and have someone balance it while it is unbolted, then raise or lower the transom with the trailer jack and re-bolt the motor. I'm also told the next easiest alternative is to remove the flywheel and use a shop hoist to lift it with an eye bolt.

 

[GPI Racing]

Blue Grey,

I'll be arriving around mid-day Wed. We are bringing 6 boats. (the 140mph STV, an XB2003, a SS2000, a Venom, a V-21 and an XB 2002) Don't worry about your engine height and all. We ran ours with the short std plate that the boats came with (6") and they worked fine. Adding a lot of set back will solve one problem and create 2 bigger ones. Steer clear of the big set back deal. The XTB really doesn't need it and with your smaller motor it won't know much difference. The 3-3 1/2" height is right close with the Mag III. Plan on a simple technique to give you some reference and you'll be able to drive most any pad-v. It is hard to explain or write, for that matter...but I'll show you and you'll have some fun.

Randy

 

[Blue Gray in PA]

What are you doing tomorrow morning Randy? I'm going fishing here in PA again if you feel like driving overnight and meeting me here in the morning. :lol: In reality we will probably be more fishing than driving. Seriously though I am really looking forward to the Rally and will be happy to have some guidance. I just re-measured it and the stock setback is 6" (I think I said 5" earlier) and if the motor depth seems close, I'll give it another try if my buddy doesn't puss out again. I'll post again after we get back tomorrow evening.

P.S. I'd really like a ride in anyone's 100+ mph boat at the Rally and it seems like you might be the best bet given the big hammers you guys are bringing along.

 

[Blue Gray in PA]

No additional info to post since the weather turned sour. The waves were two feet high so we just fished which was also a bust. When I got home, I checked the engine height more accurately and found it to be 3-3/4" below the pad and leaning by .050 according to an accurate check from side to side. I corrected the "lean" and raised the motor to 2-3/4" inches below the pad which I will try again as soon as the weather cooperates.

 

[Blue Gray in PA]

OK now what happened? I went out today and it seemed like it was slower with the motor higher. I did have four people in the boat (weight equal to three cause two were small kids) versus the two men previously and I hit 55 at 5000 RPM with small waves. Did the weight and waves make that much difference? I maintained 15-18 PSI on the water pressure which is the highest I've ever gotten and it handled nicely at 50+ but even with the Hot Foot pedal on the stop, it maxed out around 5000 RPM instead of going to 6000 as it had previously. Do I need to trim it up more to achieve higher speed? I was one to two lines on the trim gauge above square with the boat but maybe I need to go up higher or wait for flat water? Any thoughts?

 

[GPI Racing]

Put your motor back where it was. It was fine there, by raising it up all you did was lose your lever arm. At your original height I've run boats over 90mph so drag is not an issue. Don't get caught up in the raise the motor, set it way back syndrome. It won't make it better. 16 days from now I'll show you how....and we'll have some fun too.

Randy

 

[Blue Gray in PA]

I'll move it back down tomorrow morning and see what the weather is like tomorrow. If it's not going to run any better, I'll leave it down for better handling in rough water. Thanks Randy - see you in TN.

 

[GPI Racing]

It's not so much for handing in the rough. It's a delicate balance between prop bite, leverage (to lift the bow), drag, prop type and motor power. I'll give you the 101 on the whole deal and it will make more sense. We have to have something to do at the rally.....

Randy

 

[Blue Gray in PA]

Sounds like a good learning session to me. I'm definitely a newbie (like you couldn't already tell) when it comes to high speed boats so I'm willing to learn whatever I can. I have read the Allison red guide book by Jim Barnes several times and sometimes the information I see here disagrees witht he book info so I like to listen to everything and see what works. This will be the first Rally for my family and me so we are definitely looking forward to some fun.