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I posted this on the Sunsation and OSO boards, but thought I'd do so here as well. Seems I'm in quite a dilema - where are those guys running 90mph+ Aggressors????? I've heard they are out there.


2001 Aggressor. Boat was water tested yesterday out in St. Louis (totally flat water). 572CID, 680 hp @ 5400 rpms, 680 ft-lbs @ 4600 rpms (flat torque all the way up to near redline). 32P Bravo1, 1.50:1. Speedo not operational, so I can not give actual speeds. I was not the one testing the boat. Bruce Dudley from OSO board did the testing - he's got a bunch of experience, and is racing F1's this season, so I value and respect his take on things.

In short, he told me that the boat developed one helluva chine walk - so unsafe that he will not hand it over to me in it's current state. Said it was not suitable for anyone to be running around in, regardless of driving experience. It was close to an ejection situation. I think he had to serious clean-out his shorts after the ride. And there was still a lot of throttle left to go.

He used a 2" shortie drive, as that was what he had laying around the shop at the time. This may account for some of the walking, but he does not believe that a std drive would calm things down too much. The boat's got 280S K-planes. The drive was not trimmed up at all - it was neutral.
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Some additional info, after talking to Bruce again. He DID drag the tabs a bit, and ran it to 5100 rpms (still had throttle left it her too!) - while he said it calmed down a bit, he say in no way would he consider it safe - said it was a barrel roll waiting to happen.

We are going to try a couple changes on Thursday. We're gonna spin a smaller prop at high rpms - 1.36:1 gearing, 28P Bravo1. Also going to go with the std drive length. Seems we have plenty of power, so we can live with some additional slip inefficiency. Anyone have comments on this? Other props to select from? Although not the correct size, Bruce has a 27 4-blade Hydro to try-out. He's gonna dig around for a 3 blade 29 Mirage+ as well.

Speedo was not connected, but the #'s work out with the chine walk that I have been told - 81-84 mph range. He was at 4600 rpms - with 12% slip, 1.50:1 ratio, and 32P prop, this works out to around 82 mph. Problem was, he couldn't drive through it (dual ram tie-in hydraulic steering) - he had the power, but things never seemed to settle down too much.


He said he felt like he was on a pogo stick - like the prop was lifting the ass out of the water, moving it a couple feet to the side, then hooking back up, etc......... a viscous (sp?) cycle.

Anyone know know's of someone that has or HAD a fast Aggressor, please have then get in touch with me, or e-mail their phone #.


(302)-292-5189 (WORK)
(410)-398-6808
(443)-553-2115


-Mark
 

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I guess I wonder why you're that surprised. I would be shocked if there were many 90+ MPH 24 foot boats regardless of builder. The fact is; is that's there no substitution for length at water line.

It took me about 2 rides to figure out that my 222 Stinger was not going to faster that about 75 MPH safely in perfect conditions. Too much chine walking.

I think if you could run at 80 mph safely in a 24 foot boat; that's a great accomplishment.

If you put this in perspective since we boat on the same water; the conditions that permit running any boat under 32 to 35 feet wide open account for about 10% of my boating time based on waves, winds and conditions.

This may not be what you're looking for; but at first blush I'd say be happy with 80 or perhaps think about getting your hull blue-printed which would probably add a few more mph.

You might also consider an extension box.

ps: I assume you put the kplanes on right?

any my other question is when can someone actually tell you you cannot have your own boat? - You say he told you "he would not hand it over to you in it's current condition".

what exactly does that mean? You can't have you boat back unless it doesn't chine walk?

- jeff
 

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Discussion Starter · #3 ·
JEFFJ said:
I guess I wonder why you're that surprised. I would be shocked if there were many 90+ MPH 24 foot boats regardless of builder. The fact is; is that's there no substitution for length at water line.

It took me about 2 rides to figure out that my 222 Stinger was not going to faster that about 75 MPH safely in perfect conditions. Too much chine walking.

I think if you could run at 80 mph safely in a 24 foot boat; that's a great accomplishment.

ps: I assume you put the kplanes on right?

any my other question is when can someone actually tell you you cannot have your own boat? - You say he told you "he would not hand it over to you in it's current condition".

what exactly does that mean? You can't have you boat back unless it doesn't chine walk?

- jeff
Jeff:

Comparing the Stinger to the Aggressor is apples to oranges, IMHO. There are 24 foot boats that run 100+ mph. Just recently talked to an OSO member that used to run an '87 Checkmate radar'd at 103 with a blown Nickson 540. He's down in the Potomac area, and conditions are generally <1' chop - not ideal conditions for chine walking.

Yes, I have K-planes.

Bruce needs to cover his ass, and I fully respect that. What *could* happen if I barrel rolled the thing this season? Not only would he feel extreme guilt, but he *could* be liable, since he knew full well about the ill handling characteristics.

We're gonna play around with props and see how much more stable we can get the boat. We've been talking about hook removal (hull mods), but that is something that will wait until we examine all prop types.

I don't plan on running 90 mph WOT for any extended period. Just like a fast bike, it's great to know you have the power and can use it for short bursts ;o)
 

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I agree the boats are different but still I think that being able to run 80's safely in a 24 foot boat is pretty good.

You may never get rid of the chine walking simply because you're pushing so much air under the hull at those speeds. A 24 foot boat has very little area for wetted surface contact and the shorter the boat (assuming a V Hull) the more likely it is to chine walk at high speeds.

I understand that he wants to give you a safe boat, but there's also a thing called a "liability waiver" or a "release of liability" that he could have you sign if he was worried that you'd roll the thing.

Putting the big tabs was certainly the right thing to do.

Maybe an extension box, working more with the x-dimension and hull blue printing will minimize the chine walking to make it safer.

I posted two articles in the Main Forum if you'd like to read up on the dynamics and causes of chine walking.

You definately need to get that squared away so that you can be the first to the marina once we leave Mike and Sue's for "Sunsation East 2002" this summer.

- jeff
 

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Not sure how this applies but in outboards the general rule is the less drive in the water the less likely the boat is to chine walk. That said, I think your problem stems from running that really big (high pitch) prop in a surfacing condition. It wants to act like a paddle wheel and push the back of the boat sideways. Any small boat that runs big numbers has to be set up properly. Make sure there is no air in your steering as this will make chine walk inevitable. I think you are on the right track with the 1.36 drive. Further expirementation with drive height is also in order. Keep us advise as to your progress. My boat is in the shop now for a major horsepower injection (Whipple install) and I will be testing in the next couple of weeks. I have a 24 Progression and it is rock solid at 80 MPH now but who knows what it will do with 200 more HP. I am running a 1.36 bravo drive and will be trying different props as well. If you can find a Spinelli prop (I think there is a 29 on OSO) it may be more stable than the Bravo, it is on my boat. Kook, give me a call if you like at 413-596-9284 and we can discuss this.


PS. THIS is the kind of thread I read the boards for. Helping (or being helped) people to get the most out of their boating experience. Thanks, Jeff, for making it possible.
 
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