Propeller truth,facts and fiction...

[2FORCEFULL]

Seems that there are lots of opinions on how propellers work, what works ,... and what doesn't, that being because of the so many different variables ..."X" dimensions one of the big ones... bottoms surface , hooks and rockers...what the boat was designed for...some boat just plain ol have a max speed...

in this thread I will try to seek out those that really know what they are talking about, and hopefully those that what answers to what they wanna know also..

[2FORCEFULL]

Defuser ring facts,,...

defuser rings were designed for through hull exhaust boats.... it is fact that they cause a loss of top end speed, loss of 1 to claims of 4mph can be gained by running the same prop without it...

but...some boats struggle to get on plane... so the ring helps the prop bite better on take off

the ring design stops air from getting forward to the blades...causing a cavitation ....works kinda like a stall converter on a car... without the ring it's like trying to go up hill from a dead stop in the rain... or worse yet.. on ice... so...like a car with different tires....props play the same roll..

getting a boat propped right is a very fruitful experience...gratification is there with a great big smile ...

[2FORCEFULL]

prop size and pitch. major difference in performance... getting it right takes some time and knowledge.. I fine tune with a vacume gauge ..

I've heard people say,... I run this prop because I can cruise 55 at 3000 rpms... but it will only go to 4200 on top end..... that is so wrong...at 3000 rpms you are sucking more fuel then you would at WOT.. it's like a motorhome going up a hill...you can get real close by just listening to the motor.. is it singing to you, or lay'n down growl'n. with a vacume gauge you can juat look to see if it making vacume.. my 270 Hallett with twins has dual vacume gauges...they say, GPH , but are just gauges that monitor motor vacume...at WOT they say 40 GPH... let off and they go to 20 GPH...I could be wrong,.. but pretty sure they don't actually measure fuel used..

out drive boats are limited to just one gear, you use the same gear to take off, as you use for top end.. they don't have a clutch to slip like a old front engine dragster.... so the prop has to slip... the idea is for the prop to slip just enough to get the boat on plane, but not enough to cavitate and blow out..again, just like a dragster..you blow the tires off it and you go no where...same again as a prop, my dragster would start hazing the tires on the big end ...same as prop slip on a boat.. so again refferance is the same... you need a good clutch guy for a dragster, and a good prop guy for your boat...

three things to look for in a prop...take off , cruise, and top end..you want to prop for max rpms, beable to cruise, but most of all... be able to get on plane..

boat builder seem to send a lot of boats out with what ever prop they have on the shelf that is close... or even wose... what ever they have in stock... I heard owners say... this is the prop they told me to use...

[2FORCEFULL]

so now with the great debate... twin motors, and prop spin direction... some say that deep V's should spin the props in... and some say spin out...and they say the same for cats...
so I guess the only way to know is trial and error?

My Hallett 270 spins them out...when and what would be the reason for the way they spin, what do you look for in performance to decide if it's right or wrong??

my Hallett w/twin 400 hp has bravo 1 24 p 4 blades. w/ defuser rings.. gets right on plane... I added 1.5 drive spacers.. it's a rocket out of the hole , and really pulls hard in the mid range...it is real sensitive to trim.. a little over neutral is all she likes...like 1 number over... I don't really have enough seat time to make an assessment as to how it handles at top end, because I have spent so much time driving the wild cat deck boat that is so stable at all speeds... the side to side rocking of a deep v is something to get used to I guess, but can be very alarming.. the hallett starts to dance a little after the mid range... could be the defuser rings are making the props try to climb to the surface...I don't know is my answer... but will find out..

[HB Vic]

I'll get to props in a min, but the whole where do you run your drive perplexes me. I mean every boat is different, unless we have the same exact setup with same trim indicator, its kind of irrelevant isn't it? The boats would have to be a mirror image of each other for this question to mean anything.

But I could be wrong :)

[2FORCEFULL]

understanding prop pitch....the fastest you could go with a 24 pitch prop, a 1.50 gear @ 5000 rpms is 76 mph...so when a guy says his boat does 80, my eyebows raise...
that would be at zero slip!!!and would be at 5280 rpms... most merc motors max right around there.. now throw in 15% slip @ 5280 rpms... the speed drops to 68 mph..so to go 80 mph the motor would be spinning 6212 rpms.... not in a stock merc power!...aint gonna happen

I have never GPS'd my hallett... and have no idea what the slip is... it has a 2 step bottom, so it has to be better than a straight bottom? right or wrong???

it feels like it's hauling ass... but I don't have facts.. so won't say how fast it goes

there are 5 things to know about prop speed..you have to know 4 out of the 5 to calculate,.. the 5..gear, pitch, rpm,slip= actual speed..for most... who cares right..
but for gear heads... the I gotta know!

you can do it with three to get a guess number, just plug in a slip number... then go out with a gps and find out the real slip number,..

it has been said, to find out how fast the boat goes, keep trimming up till you loose speed,... or crash..:redface::redface::wink:...so be careful if you try this method :captain::captain:

[2FORCEFULL]

I'll get to props in a min, but the whole where do you run your drive perplexes me. I mean every boat is different, unless we have the same exact setup with same trim indicator, its kind of irrelevant isn't it? The boats would have to be a mirror image of each other for this question to mean anything.

But I could be wrong :)

as in "X" dimension? or trim angle?? I always straight edge the drive to the boat to see where neutral trim is, on my hallett I marked the gauge... all boats should perform the best at neutral trim... and should gain top end speed trimmed up...with a lot of boats, the "X" plays a roll... neutral trim at cruise speed cause's the boat to porpoise

most boats have reference gauges... not accurate gauges..

[2FORCEFULL]

it has been said many of times.. "a guy that thinks he know something is dangerous".... I'm a dangerous MO-FO... but eager to learn...:jumping-smiley-019::jumping-smiley-019:

[HB Vic]

as in "X" dimension? or trim angle?? I always straight edge the drive to the boat to see where neutral trim is, on my hallett I marked the gauge... all boats should perform the best at neutral trim... and should gain top end speed trimmed up...with a lot of boats, the "X" plays a roll... neutral trim at cruise speed cause's the boat to porpoise

most boats have reference gauges... not accurate gauges..

I was talking trim angle, but the same can be said for X dimension imo

[2FORCEFULL]

so,..... here's where i'm at.... I added the 1.5 spacers.... the optimum drive setting when building a boat is to set the drive to where the lower cav plate is at water line (see pic) what happens though is as you go more positive trim, the plate creates drag...

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[HB Vic]

Steve maybe I missed it, but why did you add the spacer? We're you having trouble rolling over or was it cavitating? or both?

[2FORCEFULL]

on hi performance drives, they don't have the plate in front...


65490

[2FORCEFULL]

so, I'm thinking of cutting the front part of the cav plate off...any feed back????

[2FORCEFULL]

Steve maybe I missed it, but why did you add the spacer? We're you having trouble rolling over or was it cavitating? or both?

on take off you had to peddle the boat to get on plne.. it got on easy , but you could feel that the prop was slipping, then at cruse speed the same... when going to WOT...
now you can hammer it out the hole and mid range it pull hard...

but, I think it is having a neg affect on top end because of those cav plates grabbing.. I'm sure missing my ol friend brian at the real B&D marine cause he really know his shit when it comes to drives..

[2FORCEFULL]

on my boat, 270 hallett with twins, and a twin step bottom, I don't think I need any transom lift.... ??? replys welcome

[HB Vic]

1.5 sounds pretty aggressive to me. 1/2" can make a huge difference, both ways.

[2FORCEFULL]

1.5 sounds pretty aggressive to me. 1/2" can make a huge difference, both ways.

puts my prop center 1.2 below bottom of the boat, I wanna be able to pull a skier 30-35mph... and cruise 45-50 mph.. but also wanna be able to run on pin if I want with no dancing around..

so far what I've done I achieved what I wanted... but lost on the top end...I can live with that, but if I can make it all better is the goal..

[2FORCEFULL]

was hoping to get some replys from those that have tried on done this..

[hallett21]

The tabs didn't make up for the chine walking when the drives didn't have the spacers?


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[2FORCEFULL]

The tabs didn't make up for the chine walking when the drives didn't have the spacers?


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it doesn't really chine walk, and I figured it out today.. when you trim up the drives are grabbing water from the front part of the cav, plates,.. that causes that side to grab... it trys to grab one side , then the other... it's a slight weird feeling, but after looking makes sense ...once you trim up farther it kinda goes away...hard to explain... but I think I know how to fix it

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[hallett21]

Did the grabbing get worse with the new spacers? Seems that with twins you wouldn't need to drop the props as low as say a single. What was your X dimension on the single 270s?


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[2FORCEFULL]

Did the grabbing get worse with the new spacers? Seems that with twins you wouldn't need to drop the props as low as say a single. What was your X dimension on the single 270s?


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don't know the x dimention.. but the props were about 1.5 above the center v...seemed to have a lot of prop slip and they just seemed too high...I think the answer now is to remove the lower cav plate... or get new lowers.... don't wanna spend 20k to swap out the lowers though..

[HB Vic]

don't know the x dimention.. but the props were about 1.5 above the center v...seemed to have a lot of prop slip and they just seemed too high...I think the answer now is to remove the lower cav plate... or get new lowers.... don't wanna spend 20k to swap out the lowers though..

I will tell you cav plates can drastically change how a boat performs, at least cats. When I swapped to a Imo SCX a few years ago, it made my boat undriveable. The only difference we could find was the cav plate. The SCX plate is much larger than a Bravo plate. They wanted to cut it down and have me try that. I respectfully declined, and was fortunate enough to get a full refund from Imco. Didn't really want to be a guinea pig. And as it turned out, found another guy who had his boat built with one and it did the same exact thing. So, cav plates can make a huge difference one way or the other. Thing is to find out which way to go lol

[2FORCEFULL]

well... this is the way I went....lol..no turning back now....evolution

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[2FORCEFULL]

I left the cav plate above the prop so the prop will still load...:sorry::badidea::dumb_ass::action-smiley-047::shock::thumbsUp:

[2FORCEFULL]

my thinking is this,,, the back of the drive will above the water current coming off the transom... beings it's twin motor, you really don't want something try'n to dig into the water, that and it's a 2 step v bottom..

[2FORCEFULL]

any feed back on the mod??

[HB Vic]

Not much of the cav plate left lol

Have you ran it yet?


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[2FORCEFULL]

Not much of the cav plate left lol

Have you ran it yet?


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not yet, maybe mon or tue..

[jordy]

any feed back on the mod??

I"m keeping my fingers crossed that it works for you. I still think you could have fixed the issue by losing the 1.5" spacer and taking baby steps to get to the sweet spot. Now you've blown past it and have taken some pretty extreme measures to try and remedy a different problem that was created in the meantime. You'll get it figured out before you sell it though. ;-)

[2FORCEFULL]

I"m keeping my fingers crossed that it works for you. I still think you could have fixed the issue by losing the 1.5" spacer and taking baby steps to get to the sweet spot. Now you've blown past it and have taken some pretty extreme measures to try and remedy a different problem that was created in the meantime. You'll get it figured out before you sell it though. ;-)

the spacer is the easy fix, if needed...but I don't think it will be a problem as it fixed everything else....on my wifes boat... this is where the cav plate is...6570065701

[hallett21]

Running it today?


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[2FORCEFULL]

Running it today?


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I sold my suburban so had to run to havasu to get it....hopefully tomorrow...you gonna be at mead?

[jordy]

the spacer is the easy fix, if needed...but I don't think it will be a problem as it fixed everything else....on my wifes boat... this is where the cav plate is...

Different setup all the way around with a single, and it's running behind the center pod so there isn't any water for it to grab like you're having on the Hallett. Looking forward to hearing how it works.

[hallett21]

I sold my suburban so had to run to havasu to get it....hopefully tomorrow...you gonna be at mead?

Launching Thursday AM out of calville. Sorry got your PM but been running around all week.


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[2FORCEFULL]

Launching Thursday AM out of calville. Sorry got your PM but been running around all week.


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your best bet is to go to swallow...the next would be right past middle point on the left...but the upper basin gets real nasty...if you go up towards temple bar, lots of beaches on the right, but that's a long haul in a house boat...if you stay at swallow, you are right across from two bars and restaurants'...aand also the are two stores right there...the lower basin is nice and there is more going on...upper baisn stays pretty much deserted ..and the only thing up there is echo and temple bar...swallow is the number one spot and a nice sandy beach...right when you come in to mead ask for a lake map, it has all the coves...I have to go to the doctor thurs. morn, might be able to head out after and show you around...what boats are you bringing?

[2FORCEFULL]

getting ready to head out to mead to test...we'll know if it works soon...LOL and I won't lie....if I fucked up, you'll be the first to know...but even if it does work, won't be able to convince the web crawlers and trolls though...I put the ride plate on many of boats... worked ever time... but the ring leader of the boating crowd said it didn't .. so that what was believed..:lmao1::lmao1::lmao1::lmao1::lmao1: