Falling Off The Air Pack?
 

I went for years thinking my Warlock had, what felt like in the boat, a porpoise right at top end. A bit unsettling running mid 80's. Couple weeks back I was watching this vid taken by my friends and had it on full screen on my lap top. Starting at the 5 minute mark you can watch the spray retreating to the stern and then disappearing completely. It is at that point the tunnel appears to dump the air pack and the boat falls azz first back into the water and at that speed quickly repeats the process. Going frame by frame it's easy to see. Man what kind of speed did I leave on the table by slamming the brakes on like this. lol That said, my prop shaft centerline is 1 5/8" below the lowest point on my sponsons. Is it possible the Bravo 1 is causing too much stern lift causing this at speed? Plan is to hang an SCX upper with maybe a 1" shorty SC and run a Max 5 ST. Does this sound like I'd be moving in the right direction?

Too much quantum mechanics? :cool-smiley-011:
On a go fast boating site full of opinions, not even an opinion? It don't have to be the same as mine I promise. Maybe I should have mentioned I like Mobile 1 15W50 or some chit......
Really would like to know if I'm seeing what I think I'm seeing on that vid. Last try.

I have nothing of value to add but maybe this will help pull in a response.

I’ll give you my opinion.
And that is….,.Great vid ! :thumbs

S̶u̶r̶e̶ l̶o̶o̶k̶s̶ t̶o̶ m̶e̶ l̶i̶k̶e̶ t̶h̶a̶t̶ p̶o̶r̶p̶o̶i̶s̶i̶n̶g̶ i̶s̶ h̶o̶p̶p̶i̶n̶g̶ a̶n̶d̶ t̶h̶e̶n̶ u̶n̶p̶a̶c̶k̶i̶n̶g̶
but I know -25% about cats.So, i owe you a few more cents. Lol.

alright I will wade in although this is a smaller cat than I am used to. where is the trim at that speed, neg, pos or neutral? the drive is pretty deep for what we usually did on cats as you want the air to lift the boat not the drive, opposite of a vee. next is where is the CG of the boat? if it is too nose heavy you will be positive trim to carry it and if tail heavy you will be too negative and at that drive height it would lift the stern too much and dump air. cats generally hop when getting up to speed as they are not packing enough air to carry it yet but once it gets through that it should carry itself. porpoising at top speed is not a hop, it is a setup issue.

Boat is fastest at neutral trim (90* with bottom). Trimming up even slightly results in more rooster tail and less speed. Guessing on CG but it must be close as I've had it out of the water a few times and it flew level and landed just a touch stern first. Boat has always been smooth and predictable everywhere but at the very top end where it seems to dump the air pack. I called Warlock and they had me build and install fixed tunnel tabs to their exact dimensions and location, the problem did not improve. I varied them up and down a tad via turnbuckles to no avail. Thank you for your time comp and look forward to your reply.

Thought of something else that may be a clue.......when the hop starts, if I pull the throttle back slightly it settles right down.

when you ease off the throttle you remove prop force so she settles down a little. just like when you turn you dont want to chop the throttle but ease off to settle it before you turn. cats work off of opposing forces. the air is trying to lift it and the prop should be trying to push it down which is why cats should be slightly negative trim at top speed. this is why tunnel boats, and cats (bigger version of a tunnel boat) blow over, the air is lifting, the prop is pushing the nose down and when it loses prop bite and forward force the air takes over and blows the nose up. that you are neutral seems to indicate that you have too much stern lift from the prop. the tunnel tab they had you add was to try and increase tunnel pressure so my guess is it started to hop earlier trim for trim. what prop is on this? short of changing to a shorter drive you could try a prop that will give it less stern lift and see what happens.

fwiw. I dont really like bravo drives on cats as they are hydro designed to be down in the water, not near or at surface. they tend to "surf" on the surface and are not as stable. as this is a single the drive is down in a lot of crappy water down that deep. best thing would be to try and find someone with a 2" shorty that will let you try it.

Running a labbed 26p B1 1.36 gear ratio. Will be wrenching in new power blown 509 855hp so looking to go with an Imco SCX upper/SC lower and have been salivating over the Merc Max 5 ST (short tube) prop. I have a labbed 29p B1 to see where I'll need to be on pitch but was worried about the stern lift. Don't know if I have any friends who like me enough to let me try a 2" shorty. lol May just try to find one then shim down if necessary. I do appreciate your time, thanks.

i remember Sean/airpacker on here had his boat set up right and he had a blackhawk on it w about 800 hp. i dont remember what hull he had but search his name

We had an AO 26 w\ 800 HP and ran the SCX upper w/ a SC lower. I’m assuming the tunnel dimensions of these two hulls are similar but I don’t know for sure. The hull did not like the 5 blade Maximus prop. It worked best w/ standard Bravo 1 non labbed props. The most memorable experience with the prop testing was how sensitive the hull was to just a 1/2 inch difference of prop shaft centerline movements up or down achieved w/ spacers. There’s definitely a sweet spot.

https://cimg0.ibsrv.net/gimg/www.off...f66a315750.jpg

That looks to be a 2 or 3 up box ?? ^^^^

Nice set up! Curious what she ran with that power. From research and listening to Teague on Tech, the Maximus and Max5 ST are two different beasts. The Max5 ST has a bit more diameter along with a shortened tube and is designed more for cats to settle the azz end down. No stern lift. Thanks for the information it is appreciated.

3 up box w/ 1.5 inch spacer. Bought the boat w/ the box already installed. The previous owner blew up the engine testing x-dimensions so I stepped in and threw some money at it. Eddie Young did the work. We originally brought the prop down 2 inches and then settled on 1.5. Planed better with 2 inch spacer but significantly faster at WOT w/ 1.5 inch spacer.

I believe 103mph was the best I ever saw. That’s w/ 1.5 gears and 34 B1 prop. I would pull the kids skiing and tubing w/ the same setup. I’m sure we left some speed on the table because we used it as a tow boat. Cool boat though.

I remember AirPacker, big engine little boat. :) Sad story and this pic was a salute for him.

https://cimg5.ibsrv.net/gimg/www.off...668d169fe8.jpg

yea Sean was a great guy. we used to talk a couple times a week... i have a blackhawk set up for high hp and 1:36 gears and props if you decide to go that route.

I'll keep that in mind, thanks.

I can put you in touch with my friend who had a 23 WPM, he had the setup dialed in. 598 with a tunnel ram setup, best speed was 126. I am trying to recall but thought there were similarities to the hull design between it and the Warlocks. He had a 1:36 ratio with a 2" Imco shorty running a labbed Bravo. This is an old video of his boat:

SC288, please tell’m I (cfm/sb) said hi. : thumbs Thanks ! Been a long time.

Wow you're not kidding! Just from that short vid that boat looks hooked up and sounds amazing! Def wouldn't mind hearing about his setup.

deep - it sounds like pretty typical 'porpoising'. Tunnel hulls are quite susceptible to porpoising, particularly at the 'hump transition' speed. It does sound, however, that your experience is at a higher velocity than expected for your boat. There's several things that can be done to reduce the susceptibility to porpoising... check out article on 'Porpoising' here.
(Other articles on tunnel hull performance here: https://aeromarineresearch.com/perfo..._articles.html)

/jim