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Author Topic: challenger 38  (Read 4517 times)

supersonic

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challenger 38
« on: February 24, 2008, 08:31:55 PM »

Hi O.M.R.A. lads,
It seems to me that you fella's may use the Prestwich Challenger hull in various forms for offshore racing.Can anyone advise
where to fit the water pickup and type. mine has been fitted about 1/8 inch from the tip of a 50mm prop close to the hull
but does not produce the flow as I would like.

any advice would be appreciated

Dave.
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omra85

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Re: challenger 38
« Reply #1 on: February 24, 2008, 08:59:21 PM »

Hi Dave
The water pickup can be either underneath the hull, which involves fixing tubing round the bottom of the inside, (photos 1 and 2 below) or as a forward facing tube either as part of the rudder (photo 3) or you can use a seperate tube fastened to the transom which points forward into the water flow behind the hull. (You might just be able to make out the inlet tube to the left of the prop in photo 4).
I'm surprised that you're not getting the flow, as putting the tube just behind the prop was the recommended way of doing it for years (styles change!).  Make sure the tube hasn't been kinked (if for example, it was bent in a collision, and then straightened). If you blow through it, there should only be slight flow restriction.  If the tube is old or has been used in salt water, it's possible that the inside of the copper tube has corroded and formed a partial blockage. Shoving through a 'bowden' cable inner (as found on bicycle brakes) should clear it. Follow with a good squirt of WD40.
Danny
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supersonic

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Re: challenger 38
« Reply #2 on: February 24, 2008, 10:02:07 PM »

Hi danny, thanks for the info. the boat has only been run in a test tank so far (it tried to empty it !) I can only think it is too close to the prop. Everything is new and no blockages. I have tried a smaller prop with no improvement. anyway you have given me a few options to try. Thanks again,

Dave.
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martno1fan

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Re: challenger 38
« Reply #3 on: February 26, 2008, 12:52:33 AM »

if you plan on using a prop blast piccup it needs to be at ten past two as looking at the prop from the back  O0,myself id get a rudder with built in piccups.failing that try epoxying a piccup tube on the trailing edge of the rudder you will get more than enough water flow from that ive got one on mine,works well.thats how they all used to be done before they invented the ones built into the rudder blade.
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ids987

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Re: challenger 38
« Reply #4 on: February 26, 2008, 04:16:15 PM »

Hi danny, thanks for the info. the boat has only been run in a test tank so far (it tried to empty it !) I can only think it is too close to the prop. Everything is new and no blockages. I have tried a smaller prop with no improvement. anyway you have given me a few options to try. Thanks again,

Dave.

Dave,

When you say run in a test tank, do you mean that you were trying it with the boat stationary ?
This really won't have the same effect as running it on water. The prop won't work in the same way (little or no cavitation, the engine won't rev freely either), and the pick up is meant to be travelling forward into the spray.
I would try it on the water and do a couple of quick near passes - checking for visible signs of cooling, then bring it in and check the engine temperature. If all is well so far, try a longer run. Remember, if it's a nitro engine - especially an "ABC" piston/liner engine, it is supposed to get fairly hot. Just too hot to comfortably touch the head after a flat out run is a reasonable gauge.

Apologies if I misunderstood......

Ian
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ids987

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Re: challenger 38
« Reply #5 on: February 26, 2008, 04:52:46 PM »

Dave,

Just noticed from one of your other posts that you are probably talking about the Prestwich Challenger 38. I think we all assumed that you were talking about one of the Aeromarine Challenger hulls. The significant difference being that your boat is presumably a submerged drive setup, whereas the Aeromarine Challengers are normally surface drive.
Behind the prop, and the underneath the hull system which Danny described are probably the most common arrangements for submerged drive setups. Behind the prop can either be one of the purpose built pickups which stand proud and bend forwards towards the prop, or the underneath the hull system can be implemented with the tube cut into the keel line - behind the prop. This kind of arrangement - whether the tube is on the keel line behind the prop, or to one side (or one each side like Danny's photo, where one is for cooling of the exhaust), can usually be cut to be almost flush with the hull - which reduces drag. Any of these rely much more on motion than propwash, so static testing won't really tell you much.
Rudder pickups and behind the transom pickups are usually only used on surface drive boats - or at least with an outboard rudder (in the case of rudder pickups).

Ian
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supersonic

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Re: challenger 38
« Reply #6 on: February 26, 2008, 06:07:25 PM »

Ian,So as not to be confused,yes it is a prestwich challenger 38 with submerged drive, shallow angle -- prop very close to the hull
and built with Dave Marles suggested measurements. A standard plastic water scoop is fitted close to the hull and close to the tip of the prop,on the centre line of the hull. There are no blockages in the system and the water does reach the engine head.
The flow rate is more like an intermittent dribble which is why I am concerned. If it was a strong flow then it can be restricted as required. Could it be the pickup is too close to the prop ?

Dave
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martno1fan

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Re: challenger 38
« Reply #7 on: February 26, 2008, 06:36:05 PM »

You say the water is just a trickle have you run the boat in the lake yet? it wont flow in a test tank?.Also to get good water flow you need to be doing over 15-20 mph,its the movement of the boat that creates the water flow not the prop blast itself ,although it will supply some water the forward movement of the boat is what really does it  O0.
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supersonic

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Re: challenger 38
« Reply #8 on: February 26, 2008, 07:43:26 PM »

Martno1fan,I assumed that the amount of water it threw out of my tank,even on low revs, would have been enough to feed the engine. I set my previous Huntsman in the tank to save a lot of wading when i got to the pond. I'll take your advice and try the lake as you suggest.Many thanks for your advice.-- Watch this space O0

Dave.
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martno1fan

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Re: challenger 38
« Reply #9 on: February 26, 2008, 09:41:42 PM »

No worries mate just make a close in pass to check the water flow,if alls good let her rip  O0.what motor is it? on my zen i cool the motor with one piccup but use a second for the header and pipe.
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supersonic

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Re: challenger 38
« Reply #10 on: February 27, 2008, 12:07:37 PM »

Hi Martno, -Old Iirvine 61 with a Just Engines wide manifold and purple pipe fitted low in the hull on 10% nitro, if it blows  :( I
have an old Merco 49 blackhead I can drop in. Just need some time and good weather to start playing.

Dave
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martno1fan

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Re: challenger 38
« Reply #11 on: February 27, 2008, 12:40:03 PM »

should be fine mate nitro runs a tad cooler than petrol anyway
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glennb2006

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Re: challenger 38
« Reply #12 on: February 29, 2008, 12:13:52 AM »



Here you go. (I think!) there should be a picture of a flush pick up here. I use these with success on my petrol boats, more than enough water coming through.

The bottom affair is the opposite, it is my bailer, removes water as the boat moves along. So far, so good, and does not flood the boat when it stands still.

On my older FSRV boat, I get so much water flow I have it restricted and it cools the pipe before getting to the engine to prevent overcooling.

Glenn
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supersonic

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Re: challenger 38
« Reply #13 on: February 29, 2008, 08:30:43 PM »

GLENN,Thanks for the info, I fancy that type of scoop, but think I need to get it on the pond and set up
before I modify it.
Dave.
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glennb2006

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Re: challenger 38
« Reply #14 on: February 29, 2008, 09:53:37 PM »

Always best to have a pond for set up on boats! The pick ups are easy done and cost the price of some tube and filler.

Work well so long as you fit them right, and don't get bashed in the car.

Mine start to flow water from about a fast walk pace upwards.

Glenn
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supersonic

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Re: challenger 38
« Reply #15 on: March 01, 2008, 11:03:34 PM »

OK, Glenn.As soon as this monsoon and tornado weather finishes , she will will get her bum wet and I'll post again with hopefully
a fine result.  :)Cheers.

Dave.
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supersonic

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Re: challenger 38
« Reply #16 on: April 10, 2008, 10:35:48 PM »

No worries mate just make a close in pass to check the water flow,if alls good let her rip  O0.what motor is it? on my zen i cool the motor with one piccup but use a second for the header and pipe.
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supersonic

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Re: challenger 38
« Reply #17 on: April 10, 2008, 11:01:10 PM »

Hi, o.m.r.a, Lads
Well! The weather was ok today , so after reading Mart's post about Fleetwood MY&PBC off I went to fleetwood to test the prestwich Challenger. My worries about the boat not picking up enough water for cooling were dispelled. the first run(in the babypool) was OK with a medium pitch 49mm prop was surprising ;D, so changed the prop to a 52mm with plenty of pitch and let it loose in the big pond , {-) {-) {-) WOW ! Ran a bit rich ,first time out but that can be sorted. Hope to post a video if I can get my son to sort it ! The vid will want resizing.
Thanks again for your advice on the pickup  O0

Dave.
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martno1fan

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Re: challenger 38
« Reply #18 on: April 11, 2008, 03:22:51 PM »

Hi mate glad it went well for yaa where abouts are you from ,when i get the hydro built and ready for running maybe ill see you down there  ;).
Mart
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supersonic

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Re: challenger 38
« Reply #19 on: April 11, 2008, 05:08:59 PM »

Hi Mart,only about an hour away. SKIPTON , N,YORKS. Didnt think we could sail at fleetwood but there was no one throw us off.
Cant sail on a thursday at my local club , only electric, so thought we would have a day out !  On the last run the boat did about 15 yards on its side in a straight line. think I must have hit some flotsam cos it was handling and turning well.  no damage though.

Dave
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martno1fan

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Re: challenger 38
« Reply #20 on: April 11, 2008, 09:24:27 PM »

Hi mate  Saturdays is best at fleetwood no yacht racing  O0,Sundays is a lottery although there is the other lake with the island but ive only used a sailboat on that so far.The yachts come first on race days so best way is avoid em either early or late on Sunday or as i say Sat or through the week although you do get schooner racing the odd afternoon .
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supersonic

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Re: challenger 38
« Reply #21 on: April 11, 2008, 11:25:02 PM »

Mart, Thats worth knowing , Sometimes get a saturday off but mid week will be a friday. I'll try and catch you when you get
that big hydro wet O0

Dave.
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martno1fan

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Re: challenger 38
« Reply #22 on: April 12, 2008, 09:02:25 AM »

No worries Dave,was that your first trip to Fleetwood with the boat as i saw a guy there a few weeks ago with a similar boat but he didnt stay long as the water was a bit on the rough side and he swamped his boat.Heres a vid from the day you might catch a glimpse of his boat in the vid as mine goes past it.
http://www.youtube.com/watch?v=NNDkocDzKYI
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supersonic

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Re: challenger 38
« Reply #23 on: April 12, 2008, 02:00:38 PM »

Hi Mart,No this was it's first wetting .I don't know how it got on it's side at the end but recovered ok !

here is the short vid

<object width="425" height="350"> <param name="movie" value="http://www.youtube.com/v/nRNgiP2oiSY"> </param> <embed src="http://www.youtube.com/v/nRNgiP2oiSY" type="application/x-shockwave-flash" width="425" height="350"> </embed> </object>

if this  doesnt work:

http://uk.youtube.com/watch?v=nRNgiP2oiSY

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martno1fan

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Re: challenger 38
« Reply #24 on: April 12, 2008, 04:08:13 PM »

Seems to run ok ,looked like you hit something and the boat just ended up running on its chine rail for a few feet maybe a twig or something ?.Any pics of the boat and your setup to show rudder etc,inside pics would be good too.
Mart
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