Purpose and necessity of fins in the jet pump support?

[dsw222]

We took the pump off of my 06 Challenger 180 CS because I was only getting 35mph and the boat is supposed to do 48 or so.

I thought the impeller was going to be chewed up because the boat was cavitating out of the hole, but surprisingly the impeller and wear ring looked pretty good. We put in a Solas Concord 14/19 and new wear ring (and neoprene seal).... but noticed that the "pump support" had black stubby plastic nobs around the outer rim.

I looked it up on a parts website and it appears that the pump support had plastic fins pointing out toward the middle. I'm guessing that the previous owner sucked up something into the impeller, which then spun around and knocked off all of those plastic fins.

I am now getting 42 mph with 1 rider and a full tank, but I feel that the boat should still be doing more.

Is that part worth replacing for over $300 just to get those fins back? Would it be difficult to remove the old one, since it is stuck on with "Loctite instant gasket"?

I can't see the fins making such a huge impact on the pump efficiency that the lack of them would rob the boat of 6-7 mph... but maybe it is possible? I don't know what else could be hurting the performance that badly.

I attached a drawing to try and explain what I am talking about, and a printscreen of the part from the website.

We also changed the oil, put in new plugs, and removed the stock airbox.

I would appreciate any help!

 

[dsw222]

To add on... the previous owner also had bottom paint put on... maybe that hurts the speed?

 

[Dr Honda]

Did you get rid of the 1800?


I'm having a hard time visualizing what you are saying. But....

The stator veins stop the swirl, and force the water out. When there is some damage... it's not a big deal... but if all the veins are damaged, and there is a large gap behind the impeller... then you can get some bypass, and lose thrust.

If you need a hand... give me a yell. Or... post a pic.


The bottom paint really shouldn't make a difference in speed.



And finally... if your cavitation is bad... it could be from the carbon seal.

 

[dsw222]

Did you get rid of the 1800?


I'm having a hard time visualizing what you are saying. But....

The stator veins stop the swirl, and force the water out. When there is some damage... it's not a big deal... but if all the veins are damaged, and there is a large gap behind the impeller... then you can get some bypass, and lose thrust.

If you need a hand... give me a yell. Or... post a pic.


The bottom paint really shouldn't make a difference in speed.



And finally... if your cavitation is bad... it could be from the carbon seal.

Thanks for the reply Doc, good to hear from you. Hope all is well with the fam and Islandia!

Yep, I sold the 1800 in May. I wanted something with a little more interior room that would still fit in my garage, be a little newer, and be easier on gas (and no more burning oil). I loved the 1800, but the 180 is a bit more spacious due to the wide beam. I do miss having a sunpad on the back, but the bow filler cushion is pretty cool.

If you look at SeaDooWarehouse's diagram ( http://fiche.seadoowarehouse.com/se...a=70&b=13&c=0&d=-PROPULSION-SYSTEM---INTERNAL ), part number 1 is the "pump support" I am talking about. Each of those little plastic fins that extend from the circular housing are knocked off.

Note that these are NOT the veins in the actual external pump housing... those are on part number 1 of this diagram ( http://fiche.seadoowarehouse.com/se...a=70&b=14&c=0&d=-PROPULSION-SYSTEM---EXTERNAL ). The part I am talking about is glued to the boat with black sealant

Some guys over at GH forum said that the fins either need to be fully there, or fully sanded down.... anything in between causes disturbance in the water so less performance. But even that shouldn't knock off 5-6mph. My fins are sanded down pretty smooth too.

So I did some research on bottom paint, and apparently a lot of people say that it can scrub 5+mph off a boat. I attached a pic.... mine is coming off and showing primer (the white paint literally rubs off in my hand when i touch it), the primer chips off easily with my fingernail, and theres another layer of something below that feels almost like rubber cement (and can also be scratched off). I don't know much about bottom paint, but it looks like someone did a pretty crappy job on mine (previous owner only had it one season after the original owner, and he kept it docked on Erie for that one summer)

I am considering removing the bottom paint to see if that helps.... What's your opinion?

The boat has 45 or so hours and its a 2006, so I feel like it can't be low compression or something serious like that. I dunno....

 

[Dr Honda]

OK... Now I see what you mean. It's the veins in the shoe. As you have been told... if they are damaged... just remove them. They do help feed the impeller a better "Laminar" type flow of water... but PWC and Jet Boats have done just fine without them. But... if they are half in there... and damaged... they will cause turbulence/cavitation.


OK... so where did your top speed go???? Hummm.....



I really don't think the bottom paint has that much drag. If it's up on the trailer... sand it side to side (starboard to port direction) with rough paper. That will cause small vortices, and keep surface tension to a minimum.

And... again... if you have cavitaion... then I would be suspect of the carbon seal. (try the zip-tie trick) A small leak at speed, can reduce pump pressure.


And finally... did you install the impeller? Did you verify the pitch, or the part number?



FYI... the Fam is doing fine. My 7 year old is nutz... but I'm sure she will be better soon. (as she gets older) The Islandia is running well and all my welds are holding on the engine. (knock on wood) If you are going to be local for a ride... shoot me a txt, and I'll try to hook up with you. Also... I'm just digging out of my normal spring time rush... so if you want a second set of eyes to look over the parts... let me know.

 

[Dr Honda]

One more thing... what's your full throttle RPM's. Are they low too?


Something else to think about..........


1) It is just a little less power than your old boat.

2) it only has one pump. (less thrust area)

3) It's heavier

4) It has a poor aspect ratio. (it's fatter than your 1800)


All of that leads to less speed than your 1800. So... do we have a verification of a top speed? Or is this just assuming it should be in the low 50's? (I'll see what I can find)


Oh... is this with the top up or down? I know the top will scrub a good +5 mph off the top speed.

 

[dsw222]

I really don't think the bottom paint has that much drag. If it's up on the trailer... sand it side to side (starboard to port direction) with rough paper. That will cause small vortices, and keep surface tension to a minimum.

And... again... if you have cavitaion... then I would be suspect of the carbon seal. (try the zip-tie trick) A small leak at speed, can reduce pump pressure.


And finally... did you install the impeller? Did you verify the pitch, or the part number?

The reason i'm concerned with the bottom paint is because if i just press my finger tip on the paint, my finger will be stained white with paint. Its almost like the white coat of paint isn't sticking to the grey primer coat (which is why the gray shows through in so many areas). In my opinion, it comes off wayyy too easily

I have not done anything with the carbon seal. Do you happen to know of any posts to link me that have how-to's of checking this or doing the zip tie trick? I'm still searching here but haven't found it yet.

My buddy in Monaca buys skis and rebuilds them, then sells them. He did the impeller and wear ring swap for me. The replacement was a Solas Concord 14/19, it looked to be the right part but i didnt measure pitch. We put in a new neoprene seal too, greased the cone, and he said my bearings were in good shape.

My max RPM's are just over 8000 as the boat is accelerating... then at max speed they hang around 7800. The manual states it should be 8000 RPM. I would have thought that the impeller pitch was hurting my RPMs... but it also hung at 7800 with the stock impeller.

Before the swap, I was getting 35mph, and now I am getting 42mph on GPS. BoatTest stated a max speed of 46 in choppy water, and several forum posts state mid to high 40's GPS... So I thought with a better than stock impeller and an air intake, it should be at least as good as 46. The bimini top was not up for any numbers, but i removed the windshield (it doesnt fit in my garage with the windshield on)... i dont think that would affect speed though. The oil level is perfect (we did oil, filter, plugs) so that isnt affecting RPMs

These are some quotes from other boards about bottom paint, which is why I suspected it.... but i don't have any experience with it, so I have no idea if its worth the effort of removing or not. It sounds like a royal pain to remove, and Fox Chapel Marina quoted me at $3500 to have it buffed off (HAAAA!!!). Still calling around other marinas to get pricing. But I have my doubts about how much it affects speed too

-----

"Yup, 5-6mph on pretty much any boat. Standard complaint from any owner who wasn't informed on this before he asked his painter..."

"everything I have seen is about 5 mph loss on everything with std bottom paint..now they have some super slick paints that may not hurt as much, just don't know anybody who's tried them"

"I went from a 41 mph boat with paint to a 45-46 mph boat without paint. Cruise at 30mph dropped the rpm 300-400rpms without paint as well"

 

[Dr Honda]

The anti-fouling "Bottom" paint is soft. That's the point of it. So... when muscles, or barnacles attach... they can be scrapped off very easy. OR... they come off with speed.

As far as the loss of speed.... OK. I never had any personal experience with bottom paint, since I don't leave my toys in the water. But, I have worked on/with enough boats that it was never brought up before. (especially when I was still in SoCal) Generally... a rough surface is BETTER for speed since it breaks surface tension. (that's partly why they dimple a golf ball)


I was sitting here, eating my sandwich... and I was over on SDSB... and I was seeing speeds all over the map. Some guys said high 30's... some said right at 50... but most were in the 40's. So... who knows.


7800 to 8000 RPM is right. As I recall... 8200 is where your revlimiter is set.


Ummmmmmm.......


Did you have the supercharger rebuilt yet?? When you put on the new air box/filter... did you check the supercharger for slippage?


As for the zip tie trick... just put a fat ziptie around the rubber boot holding the carbon ring. (in one of the valleys) it will help reduce any vibration... and it will also help keep the boot from being sucked back. (I can TXT or post a pic later, if the rain is one when I get home)

 

[dsw222]

Hmmm it probably isn't the paint then. I may end up removing it eventually anyway because it looks like hell sitting on the trailer (or maybe at least slapping some more paint on it)

The supercharger was rebuilt with the steel washers in 2011 (he gave me a receipt for the work)... but i did not check the slip. I will put this on the to-do list along with the carbon seal trick, then report back!

 

[Dr Honda]

That soft, anti-fouling paint has to be removed before you can re-paint with anything real.


I'm not saying the supercharger is slipping, because you are getting real close to the RPM spec. But... I figured if you had your had in it... you can check.


Oh.... double check all the fittings between the supercharger, and the intake plenum. If you have an air (pressure) leak... you will lose a little power.

 

[get_real]

Bottom paint does slow down watercraft as compared to slick fiberglass. Unless you leave it in the water for long periods, I would definitly remove that paint!