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geeviam

Improved Cheese Grater

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I'll kick off this thread with what I've done so far, to make a modified cheese grater plate that will pickup enough water in the sea chest for proper live well circulation, and also fit flush with the running surface of the hull to improve high speed performance and stability.  On the first attempt, I made new grater plate out of 3/8" thick Lexan which mounted flush with the bottom of the hull.  A table saw was used to make angled cuts to match the angled shape of the sea chest opening.  It took a lot of time and saw blade adjustments to get the cuts angled right, so that there are no gaps.  It performed better than the factory grater plate.  However, I drilled too many holes that were also too large, so some drag and turbulence was still there.  Here is the second generation cheese grater.  There are only four 5/32" angled holes in it to pick up water, but the water flow with or without the pump turned on is just fine.  The holes are all along the right side of the sea chest, farthest from the keel and away from the prop.  I did not get the same speed gains that others have claimed recently, with a modified grater plate.  But, the all-around improvements in performance, handling, stability, fuel economy, prop slip, and even porpoising, are remarkable!  No more white knuckles and constant ride/trim tweaking.  It is like a new boat and very fun to drive!  There's only one thing yet to fix... when the boat is pulled out of the water, the sea chest holds a little water on the side that has no holes in the cheese grater, because it's lower on the vee of the hull.  One tiny drain hole on that side should do the trick.

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Nice post Geeviam.  Just curious, what we’re the speed gains if any that you experienced.  I’ve experienced quite a bit of porposing on my 21 MA which seems pretty common, but wondering if this may help with that as well.  Good work

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45 minutes ago, Inshore1 said:

Nice post Geeviam.  Just curious, what we’re the speed gains if any that you experienced.  I’ve experienced quite a bit of porposing on my 21 MA which seems pretty common, but wondering if this may help with that as well.  Good work

Thanks.  I can't say for sure how much faster it was, because I unknowingly turned off high-accuracy mode on my GPS before the test run.  It felt like 2 mph faster.  I may run the boat again on Wednesday if weather permits, and get an accurate speed reading.  Just gotta say - this modification was worth the effort.  I was cruising at 4200 rpm getting 7.4 mpg, and not needing to use tabs at all, to keep it stable.  That was a thrilling new experience!

 

17 minutes ago, VsteveV said:

That is remarkable. Which RF?

RF 16 with a 115 SHO

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So as part of the modifications, the trim tabs were raised as high as they could go in the recessed pockets. In addition, the live well grate was made as close to flush as possible. Slip was GREATLY reduced, and as most of you saw the speed increase was massive

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Geeviam, that is awesome to hear on how it changed the boat. Great fab work by the way. 

In the spirit of top speed, my SCB doesn't even have a high speed pickup. No pickups=no drag. I don't fish live bait so it doesn't bother me, and I have recirculating pumps anyways for long runs. 

On my lake and bay, removing the 2 clamshell pickups gained 5 mph, but their locations were awful

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Nice work guys!  I really like the lexan as I would think it would hold up better than most and not want to deform.

The question I have is the turbulence coming from the hole design of the grater or it not being flush?  I have 3 wells that pickup water from the sea chest so it would need flow, I really only use one if any.  Also, what kind of pressure is the sea chest under from water coming in at speed?  My guess is that the large holes toward the rear of the grater are to allow the pressure out. 

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14 hours ago, geeviam said:

But, the all-around improvements in performance, handling, stability, fuel economy, prop slip, and even porpoising, are remarkable! 

PRICELESS!!!

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1 hour ago, mulligan said:

Nice work guys!  I really like the lexan as I would think it would hold up better than most and not want to deform.

The question I have is the turbulence coming from the hole design of the grater or it not being flush?  I have 3 wells that pickup water from the sea chest so it would need flow, I really only use one if any.  Also, what kind of pressure is the sea chest under from water coming in at speed?  My guess is that the large holes toward the rear of the grater are to allow the pressure out. 

I think the turbulence comes from a combination of both - not being flush and the number of holes.  I agree with you, that the larger holes equalize the pressure.  But the larger holes are also like dragging a parachute down there, especially with the rear part of the factory plate sunk-in and not flush.  I think it's most important that the modification makes the rear of the grater plate flush - more so than the front of the grater plate.  My new plate is barely recessed in the front, and totally flush in the back.  That's just the way the sea chest cavity is molded on mine.  I think of it as a mini-stepped portion of the hull, so I'm ok with it.  I was surprised how good the pressure was with just (4) 5/32" angled holes in it.  I figured - start with the least amount of holes and try it first.  You can always drill more.

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How does the well work when not running. Only having 4 small holes for intake would seem to restrict flow. I have 2 pumps feeding the main well. 1100 and 800 GPH. Not sure those 4 holes would provide enough free area for intake at rest.

 

Nice fab job.

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1 hour ago, geeviam said:

I think the turbulence comes from a combination of both - not being flush and the number of holes.  I agree with you, that the larger holes equalize the pressure.  But the larger holes are also like dragging a parachute down there, especially with the rear part of the factory plate sunk-in and not flush.  I think it's most important that the modification makes the rear of the grater plate flush - more so than the front of the grater plate.  My new plate is barely recessed in the front, and totally flush in the back.  That's just the way the sea chest cavity is molded on mine.  I think of it as a mini-stepped portion of the hull, so I'm ok with it.  I was surprised how good the pressure was with just (4) 5/32" angled holes in it.  I figured - start with the least amount of holes and try it first.  You can always drill more.

So if I am understanding you, the issue was not one of the plate protruding "below" the hull, but being "recessed" or "inset" to the hull, which caused the unwanted turbulence and slower speeds, etc.........I guess primarily at the aft end of the plate    I had been confused because on my Pathfinder, the standard SS factory plate is recessed.  And I didn't see how changing out or modifying my plate would provide any benefit because it was already recessed.   I had it all bassackwards!  So, you are saying the slight recess at the aft end of the plate was robbing the boat of better performance.  It is just hard  for my little pea brain to accept the fact that that little bitty lip could cause a speed loss of several miler per hour.  If I am understanding you correctly............ 

If this is all true, this could make for a pretty profitable little side business........considering how many thousands and thousands of Mavs, Hewes, and Pathys are on the water!  I will certainly line up to buy one if somebody wants to make me one.  If I could buy a replacement grate for say, $100, to gain 2 mph on top end, I would jump all over it.  The other performance gains would be just gravy!   (I have a buddy, who happens to own a 24 Pathfinder, who also happens to own a pretty nice machine shop!  I might have to pitch the idea to him, if the performance gains are serious enough.)

 

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2 hours ago, Capt. Troy said:

How does the well work when not running. Only having 4 small holes for intake would seem to restrict flow. I have 2 pumps feeding the main well. 1100 and 800 GPH. Not sure those 4 holes would provide enough free area for intake at rest.

 

Nice fab job.

Troy,

looking at the one Linesider159 did looks to have more holes and he had a performance increase. Also, Geeviam says he started with small holes and could make them larger if needed. Y

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5 minutes ago, lurem said:

Troy,

looking at the one Linesider159 did looks to have more holes and he had a performance increase. Also, Geeviam says he started with small holes and could make them larger if needed. Y

Saw that!

I think the performance gains will come from the more flush mounting of the plate. Eliminating the lip on the leading edge that is creating drag. I wonder if you could glass and sand that area totally true to the bottom.

It would be Interesting to fair that plate to the bottom of the hull to make it totally true to the running surface. I ripped one off one day on the old boat. It slowed me way down and made the boat squirrelly.  It also created a siphon and sucked all the water out of the well and killed all my bait.

 

Curious as to the no relief holes at the back. Got to be a lot a pressure at 60 plus MPH on that plate.

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a few of us are in the 50 mph club and can test ours once built, why don't you get one and be the 60 mph club test dummy, er guy!! haha

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15 minutes ago, Capt. Troy said:

It would be Interesting to fair that plate to the bottom of the hull to make it totally true to the running surface

That is what plan was, keep the plate, recess the screws, and make flush by building up inside the chest.  But then working with a sheet of polycarbonate would be easier and less itchy. 

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3 hours ago, Capt. Troy said:

How does the well work when not running. Only having 4 small holes for intake would seem to restrict flow. I have 2 pumps feeding the main well. 1100 and 800 GPH. Not sure those 4 holes would provide enough free area for intake at rest.

 

Nice fab job.

I was surprised that I saw such good pressure with only the four small holes, while running with the pump off, and even better with the pump on.  I have only one pump and one live well though.  I think the angle of the drilled holes makes a difference on drag and pressure too.  Linesider's photos show more holes, but they are drilled straight up (vertical) instead of angled like mine.  That may be the reason his plate with many more holes does not create as much drag.  My plate's holes are drilled at an extreme angle to pickup water without needing the pump to push the water to the well.  Not saying mine is better - in fact, Linesider's is probably better if maximum speed is the goal.

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9 hours ago, Capt. Troy said:

Curious as to the no relief holes at the back. Got to be a lot a pressure at 60 plus MPH on that plate.

Here are some pics of my first attempt at an improved grater plate.  Too many larger angled holes created more drag.  It also had pressure relief holes angled in the opposite direction up front.  The new version with four small holes on one side creates more water pressure than this one did, with less turbulence in line with the prop.  I don't think the new version creates an alarming amount of water pressure on my boat, since maximum speed is around 52 mph.

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3 hours ago, JEM said:

So, you are saying the slight recess at the aft end of the plate was robbing the boat of better performance.

Yes JEM.  The difference on mine, at the aft end, was about 5/16".  That plus the large holes at the aft end, was enough drag to cause instability and loss of performance at higher speeds, IMO.  Before I started this project, I mounted my cell phone on the console and shot some video of the boat running/porpoising.  When I watched the video in slow motion, I noticed the porpoising was actually a circulating, oscillating motion with side-to-side as well as up-down action.  My thought was, the "drag and catch" of the cheese grater on one side of the boat was causing the instability.  I am very happy with the outcome!  Like a kid with a new toy!  I love my new boat! :D

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This would be a very, very simple product for a machine shop to manufacture.  The shop could buy the lexan in large quantities, mill it down and drill the holes with a CNC machine, and presto, finished product for sale in minutes.......literally!   The only research left unfinished at this point are the optimal sizes, configuration, and placement of the holes. 

Wonder why MBG wouldn't want to check into this to gain a few extra mph for their performance bulletins and to sell for retrofitting by customers?  $34.29 for the old style, SS model grate, and $68.99 for the new style, high performance Lexan grate. 

People spend hundreds and hundreds of dollars doing the prop dance trying to eke out an extra mile an hour, so what's $50 or $75, or even a $100,  for a sure fire, no brainer, performance enhancement?

Now, it makes me wonder if my low profile, bronze thru hull transducer affected my performance any?   LOL 

 

 

  

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I would like to place a order for one Gary M hi performance cheese grater, for a 2010 HPX . I wanted the smoked clear lean model . 

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5 minutes ago, dabear said:

I would like to place a order for one Gary M hi performance cheese grater, for a 2010 HPX . I wanted the smoked clear lean model . 

LOL! Absolutely Joe - order taken!  But it'll cost you one fishing trip on that HPX18-V, and maybe a case of that "Snook Elbow" you've been complaining about.  :D

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Maybe someone who designed the original can chime in, Skip?

To me it sounds like everyone has a lip toward the rear of the grater.  I would think this is to create a negative pressure to pull water through the sea chest giving more flow but also creating turbulence and not perform as good from a performance standpoint but would work well of you are like Capt.Troy who has a sump pump feeding his well.:D

Then you have Geeviam whos would work great for boat performance and be able to feed a well but might struggle to flow enough if you have to run multiple pumps. It would be fun to play with these things if mine was not sitting over my trailer bunks.

But what do I know, I grow grass for a living. 

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After seeing and hearing the results of Linesider's design, I think maybe a combination of both hole types would work for the boats that need to pickup more water to feed larger well space and/or multiple pumps.  I only have a single well with a single pump, so the four small angled holes work fine for me while running or at rest.  But, if I had the need for more water volume, without creating additional drag or turbulence, I would try drilling one more row of straight (vertical/perpendicular) holes like Linesider's grater plate has, and not drill any more angled holes.  IMO, the angled holes that scoop up the water create some drag, but a few are needed for some pressure to keep the pumps and hoses primed.  The only down side with the additional row of vertical holes might be that they will equalize some pressure so the pumps will have to to be powered on while under way.  But, the up side is the pumps should stay primed and push a lot more water to the well(s).  Just throwing in ideas...

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