kwiktsi

OK, it was recommended to me to run a 7015/3 prop on my BJ55 so I got one and tried it out. The motor will not pull it and it never unloads- unless I am making a wide right turn, then it starts to unload and haul butt- until I straighten out again and then it slows back down . It also prop walks very bad. I brought the strut up as high as it would go, which is only about 1/8", if that from where it was and it helped a little, but still nowhere near what it should be. The boat is all stock and I am told it should be able to pull it and to check the setup. My question is can it actually pull this prop in smooth water? Should I open the strut hole and raise it higher? I don't want to adversely effect the handling but raising it too high just to spin a bigger prop.

I actually had my first blowover yesterday trying to make this prop work- I had the strut all the way up with a fair amount of upward thrust to it trying to unload the thing and while making a long right turn, it kicked up into high gear, "skated" through the turn on just the prop- it was booking pretty good, but started nosing up. By the time I let off, it was too late. I can tell you one thing- when a 55" boat blows over- it is impressive! That thing get's points for altitude and hang time lol. It went over about 220 degrees, hit the top of the left sponson on the water, knocking it back in the air again and somehow landed right side up but stalled so I had to get my inflatable raft and row my butt halfway across the lake to get it lol. The bad part is you know the whole sight/sound delay thing at a distance? It landed and I just thought "whew, that wasn't too bad", THEN I heard the loud impact- it put a few pretty nasty stress cracks in the bottom side from the impact . My night was spent fiberglassing when I got home.

Anyway, back to the prop- another option offered to me is a Texas cut 275- which would be the better choice here? Thanks.
Joe

rcboateric

A stock 7015 prop(no cupped) is a small size and pitched prop, the stock pitch is 70mm Dim. x 4.13" pitch, your engine should unload it very easy, make sure the pipe length is proper, you might extend the pipe length to 12" or 12-1/2" and see how it goes.


http://rcprops.com/rcprops/29.html

kwiktsi

The prop I have is a 7015/3- not 2. I just don't see if having the power to pull it, not going by my first runs. Not without raising the strut way up and having to relocate the stuffing box up a bit as well to line up with the higher strut. I also don't want to kill the handling of the boat by raising the strut that high.

My pipe is the stock one, extended as far out as it will go- which is just about 12". If I go any further, the O-ring will be off the edge of the header.

I'm sure it can be made to work, but this boat isn't worth the time or money to mod it or relocate the stuffing box. Any thoughts here? Ahh, screw it- maybe I'll just buy a ported cylinder and piston and see if that helps any .

rcboateric

If your cat blowed off at the flat water, that means the strut level can't go up any more, what was the water condition when your cat was blowing off?

kwiktsi

It was like glass- BUT I had the strut with a lot of upwards thrust to try to unload the prop. I don't think it would have blown off with it level. With it level, it will need to come up quite a bit to get this prop to work- probably about 1/2" at least from the bottom of the sponsons to the bottom of the strut. Is this going to be too much?

rcboateric

You might add 5-8 oz of the weight to front side of the cat to keep its nose down, my strut height is about 1/2" to 5/8" that from the bottom of the sponson to bottom of the brass tube, keep raise the strut(flat angle) 1/16" by 1/16" until your engine unload that prop.

kwiktsi

I'll give that a shot then, just stinks because I'll have to either remove the stuffing box and reposition it or try to bend it without cracking the boat since it will not line up with the strut if I bring it up higher.

As for the weight in the nose- I'm hoping I won't have to if the prop is level, but we'll see what happens. Thanks for the help Eric.
Joe

rcboateric

No problem joe, and this is the only way to resolve low CG issue without blowing off your boat.

glennb2006

I run one with success on my mono, it works really well, but, it needs to be quite high up the transom to be effective, 13mm from tip of vee to centreline of drive.

Not sure it is a good prop for a cat.

My motor is tuned, this prop spins in excess of 18500 RPM with ease.

If you don't want the prop, drop me a PM and we can do a deal, I'll buy it off you if the price is right!!


Glenn

rcboateric

7015 is a fast but not the fastest prop for a cat hull, I saw one that ran with a QD engine on a small size cat, I was very impressed. I have a 7521 cupped rigger prop, the prop didn't show any specs but I guess it has 5.7" to 6" of the pitched, even for this big pitched prop, my engine would unload it easily once I raised the prop a bit.

kwiktsi

Sorry Glenn, if it doesn't work- dasboata is going to make good on it since he recommended it and sold it to me for this boat. I'm not eating a $70 prop . So far he seems to be willing to help, I just wanted a second opinion since I am not completely convinced it is the best for this setup.
Joe

glennb2006

No worries,


I know they are not cheap - was going to help you out by taking it off you, but if Chris is going to take it back then that's great. Good customer service too.

Try it with different strut heights, you might find a good position for it.

Glenn

kwiktsi

He is willing to do what it takes to make it right, I'll give him that.

I'll play with the strut, just sucks because my stuffing box/brass tube sits too low to go higher than the stock strut slot would allow. Now that I had to open up the slot more to get more height out of it, I'm having a bear of a time getting the tube to cooperate . I'm just thinking a smaller prop would have been a better choice with the stock strut adjustment range. No worries though, if I can't get it to work by raising it a bit, I'll mod the motor to MAKE it spin it LOL .
Joe

rcboateric

You might send it back to chris and let him remove some pitch out or switch it to a 6516/3, Is it a round ear prop?

kwiktsi

he asked me if I wanted him to remove some pitch, I just don't know what the best way to go about it is. I asked if they had a smaller 3 blade that would work better, but he never answered. I'm assuming the 6516/3 would probably work a bit better without having to raise the strut to the sky? What would be a better option- having some pitch removed from this one, raising the strut and using it as-is or going with a 6516? Thanks again for the help Eric. Chris seemed offended that I questioned this prop working since it certainly wasn't in the boats stock configuration.

MrMikeG

Ask Dasboata to swap it for a 7015/2 that is a better prop for you.

black talon

My Feedback: (5)

i tried a 7016 2 and i got more out of the original prather 270. now i run an octura x 472 detongued and barr cut. i think thats about all that the stocker will push.

kwiktsi

See, I told him initially that I had heard a 72 is a good size for this boat, but he said this one would be better. Once I realized it wouldn't work, he said to raise the strut because it has to work on this boat, we went back and forth with me asking questions- specifically about raising the strut so high and any adverse effects on handling without getting any real answers, then he ended up saying he has no time for this, told me about all his victories and that my boat is a POS lol. That's why I kind of let the customer service comment slide last night. He did say he'll do whatever I want to do- but I went to him since he is the expert and I wanted HIS advice, I didn't want to figure it out on my own since I have no clue. I wanted something that would work on a 100% stock blackjack with good results- nothing more, nothing less and figured someone with more experience than I could recommend that with no problem.

Oh well. I'll try to raise the strut more like I said, I just don't want to have other problems because of it like the boat being unstable or anything. If that doesn't work, maybe I'll send it in to have some pitch removed or something. I just don't like the idea of messing around with it if it's not going to work- with my luck, something will happen in transport or something to knick it and I won't be able to exchange it. Just wanted to put a prop on and be done, not change the whole boat to work around a prop.

glennb2006

Kwitski,

whenever you make a major change like swapping a prop, it is inevitable that for good performance you are going to have to make strut adjustments.

I can change props and end up with an unuseable boat as a result unles I reset the strut.

Glenn

rcboateric

You might send it back to chris to reduce the pitch a bit, I'm sure your engine will spin it after that change. BTW, How fast can your cat run with a original prop(2.74 x 4.2 in bronze)?

kwiktsi

I understand that- but this is higher than the stock strut would allow- I had to open up the strut slot quite a bit and bend the stuff box up a ways to get it higher than it would go stock. I don't mind at all, but I don't want an uncontrollable boat due to it being up so high either so that was another concern. This isn't a race boat, it is a play toy for when I go up to the lake here with our real boat and I didn't want it to snowball into a "hot" setup either. One way or another, I should be able to get it to work, I guess..

kwiktsi

I brought the strut up today, so I'll see how it likes that. I can't go any higher than where I have it now (about 5/16" to the bottom of the strut) without completely removing the stuffing box and redoing it's exit angle. Even where it is now has more "side load" on the shaft than I'd like (pulling up against the stuffing box, creating extra friction) pulling the strut so high from stock. On that note also- how much pressure against the stuffing box/flex is safe? It is teflon lined, but I still don't like it being tight to spin like this.

I don't really want to tear the boat apart just to make an oversized prop work, so if it doesn't work like this, then I'll have to have the prop modified or swapped out.

Top speed on the other prop in glass conditions with the strut a little under 1/8" was 39-40mph on GPS, I flipped the boat and lost my GPS before I got to make adjustments to try to get more .

rcboateric

Don't worry about that friction if you're using the synthetice grease, I have a shaft that has been using almost 2 years in my boat and it still looks like new.

black talon

My Feedback: (5)

with my strut even with the stuffing tube and the 472 i get 42mph. what i would worry about on your setup would be premature wear of the stuffing tube or the flex cable coiling up and taking out your drivetrain. i don't know if coiling is a problem with square drives. good luck, i'm still feeling my way thru the dark on mine too.

MrMikeG

The BJ55 isn't a race boat, I doubt Chris has had much experience with one. I don't have one ether but I have both props I recommended and have been running cats for about 8 years. The 7015/3 is much harder to pull than a 7015/2, ask him to exchange it for a 7015/2 and I bet you will bolt it on and go, no doubt in my mind.