XTB21 with Yamaha 175 Vmax SHO

[Christofer]

Hi everyone,

Thanks for the add and a great looking forum and community!

I picked up probably the only Allison in my country - Norway (Europe, that is) a couple of years ago; an older XTB21 that had been brought here and restored a few years back after having originally "seen better days" and been laid off to rot for some time outside somewehere back in the US. Having known about these boats since my youth from forums such as screamanndfly.com etc. - once I saw the boat advertized for sale here and never having seen one first hand - I just called the guy and said I'll take it!

I bought it with no engine and in a condition that caused me to do quite some work on it, but wasn't too bad to have a project during the pandemic anyways... So it was actually just shy of two years form buying it before finally hitting the water last summer. The interior has been modified by former owner so might look a bit different than most XTB21's out there, with a center console. Former owner here had a Merc 200XS on it and owner before that a stock merc. 150 hp I believe. Having read the WavetoWave article about the Allison Grand Sport with Mercury 150 Pro XS, and with gas prices here a little above twice US prices I finally opted for the Yamaha 175 Vmax SHO, 4 stroke engine, however modified with Bobs nose-cone fitted on the lower unit and engine fitted on Bobs lift.

I haven't got around to experiment with a lot of propellers yet, but ran the first 30 hours or so on the engine last year before winter mostly with a Lexor Solas 14 1/2 x 25" prop just to get started. So far I've seen 77 mph, but hoping eventually to break into the 80's with a proper propeller. Hoping to get some pro(p) tips from here on the forum eventually, and perhaps help in sourcing one from the US market probably, as Hydromotives are few and far between around here... What I will tell you is the boat runs great so far, and basically at any speed on plane up to 65 or 70 mph the mileage is between 9 and 10,5 mpg - no kidding!

Posting a few photos of the process and end result so far, I'm pretty happy about it!
And now - spring is not too far away!

Christofer

 

[Christofer]

Few more pics from on the water..

 

[wcarlyle]

Nice job in bringing it back to life, looks like you are enjoying it. Beautiful scenery by the way, looks like a great place to boat.

 

[Ally-Sun]

Awesome job, thanks for sharing!

 

[Jessie]

Beautiful boat! Great job on the restoration.

 

[22R]

Welcome and very cool Ally. Where did the center console come from if you know? Kinda looks like a Bullet one ? You may want to get a Allison bucket seat for the driver spot. Beautiful area for sure you are in. Best of luck and keep us updated.

22R

 

[Christofer]

Thanks for the comments guys!

I actually don't know from where exactly the console came actually, it might have been made (or chopped from another type of boat) over here in Norway. When I got the boat the console was the worst part; not true / straight and definately not stiff enough. Could wiggle the steering wheel by multiple inches, how anybody dared doing that with 200XS on the back is beyond me... I had help from a local powerboat racing guy who also does grp to straighten it out and reinforcing to make it stiff, so it's all good now except for not having enough space to fit a GPS screen (its full already, haha)!

And yeah definitely have some plans to improve on seating comfort and to add a few grab handles mounted low for those on board not fortunate to have the steering wheel to hold onto! So that and getting some carpets all over is on the agenda for this season (already started making the most of the templates for carpets.)
But really I'm not sure how to get hold of the Allison bucket seats (input is very welcome ?
Alternatively I've been thinking to just re-do the simple seating upholstery that's there now (not my build) but with an improved but similar type thing including back-support and made professionally.

Other things I'm assessing or curious about is skid-planer, added buoyancy / flotation for the Bobs lift (sit's a bit low in the water) and of course props! Always lots to do and never a dull moment!

 

[22R]

You can call the Allison factory directly at 865-983-5920 and speak to Mr Bill the parts guy. Now that is the good news the bad is that a bucket seat base and custom Allison cover to go with it is probably close to a Thousand US dollars and shipping to Norway well it will be expensive for sure. You may find some used ones here in the US on facebook marketplace but the shipping will still be high. best of luck though.

22R

 

[Lotus 50]

Very cool boat. Over here it’s simple enough to buy a used prop to try it and then sell it if it’s not great. Shipping would be too expensive in your case. You could call Hydromotive and order a prop. They run Allison’s themselves. Same for Hoss.

I have a couple of Hydromotive props and a Hoss Triton, but my SS2000 is smaller then your boat.

 

[Contractor]

Nice. You got a XB 2002 now.

 

[Wave to Wave]

Very cool setup. I think that is Glen's old boat? What are your RPM with the Solas?

I really liked the ProMax prop out of the box on my Grand Sport with the 150. I think the Yamaha 175 is a great engine, and should be able to turn 6100 or 6200 RPM.

I think I ran best with the prop shaft 1/4 above the pad.

 

[Christofer]

Thanks Wave to Wave! You're correct Glen is one of the former owners. Engine selection was much based on reading your very cool article series on the Grand Sport w. 150 merc, and my own preference for Yamaha. I've modified it with Bobs cone and torque tab, as well as stiff aluminium bushings as replacement for the stock rubber rig-to-midsection dampeners on the engine and very happy with the feel and handling.

I'm eager to try more props and the promax is high on the list, but I'm also taking it nice and easy with seat time before (and between) each high or full speed test etc. Actually I did not look at my rpm gauge while doing any of the top speed runs and max value is not stored I think, but I believe actually rpm was far below 6000 most likely, certainly did not hit the rev limiter apparently. Max attained gps measured speed so far is 78 mph btw. But that does not sit right with the 25" pitch and 1:86 gear ratio adn sub 6000 rpm... I suppose the pitch of this prop may effectively be higher after having been modified or something.

I've also tried a 26 3 bladed cleaver with small hub, but the feeling with this one was not the best and actually did not test max speed, mainly due to conditions. Will try it again before returning to "get some data" for comparison. Keep you posted.

 

[Wave to Wave]

That's great Christofer, keep us posted. Did you have the bushings / mounts custom made?

Engine height and setback will be key in getting the best number. You're on the right track.

 

[Christofer]

Yes, bushings were custom made by a skilled mechanic who has done this on many race boats engines, also his own. You can imagine the "horror" still when my "new engine" was looking like the picture posted below, haha . Guess he now has "the recipe" for another engine type with the Yamaha 175 4-stroke.


Current set back is the 8" standard Bobs lift. I ran the 78 mph at close to max height considering where my lift and engine is mounted at the moment, I believe that is not at all far from 1/4" above pad actually. I'll measure exactly to see, but have no immediate plans of moving the engine at the moment. Currently I'm happy with the speed and need to get experience in managing it safely, and I like the overall handling in that it works well all round. Believe there is more speed in current setup just from maintaining full throttle for longer stints of time and perhaps tuning lift and trim ever so slightly. I haven't maintained full throttle for very long spans of time yet, maybe 15-20 seconds or so.

That said, while getting up on the pad the first times felt slightly unstable and took some getting used to, I'm amazed by the balance and stability from there on up. Near full speed it's been running very smooth and stable without need for much of corrections. I know these hulls are super-fast and thus stable even at way higher speeds, but having rigged everything myself from an empty hull I was and still am very happy that around WOT the boat is running straight as an arrow. It's just such a fun boat, pure joy at high speeds, and so responsive to any input and still manageable to own in terms of size, weight, cost etc.

 

[Brandon2684]

Throw a good 28/29 pitch prop on there I can't imagine you not doing low to maybe mid 80's