21 or 20p 4 blade

[HVAC Cruiser]

OK, I am ordering a new prop from iBoats tonight and am arguing with myself over weather or not I should drop down 1" going to a 4 blade

I started out with a 25p 3 blade which felt like to much with just my son and I on the boat.

I dropped down to a old 14 3/8 x 21p Michigan that the boat laughed at with 3 adults and 2 kids aboard.

here is my choice for the 21p 4 blade http://boatpropellers.iboats.com/Me...20527/?**********=443697269&*******=169951527

Here is the 20p http://boatpropellers.iboats.com/Me.../1143/?**********=109721354&*******=169951527


I guess my bigest question is the difference between the Solas RUBEX and the Michigan Vortex blades. the boats unladen weight is 3600. add adults and gear and were over 400#

Any sugestions on which one to pick? I have to order her tonight

 

[Barnacle_Bill]

Re: 21 or 20p 4 blade

What are your RPMs at WOT with the current setup?

 

[matts72]

Re: 21 or 20p 4 blade

I have a 21' Tahoe Q6 with the 4.3 MPI. Went from the stock 3 blade 19p to a 4 blade 18 and that was the wrong direction. RPM's where way to high. Replaced it with a Michigan Vortex 4 blade 20 and could not be happier. Good hole shot and does about 55mph trimmed up. Does about 3mph at idle on GPS. Hope this helps.

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

What are your RPMs at WOT with the current setup?

Or some info...Boat type..motor..length weight...

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Sorry for leaving out info, its a 22' Cuddy Cabin empty weight is listed as 3600# add the extra cabinet with the sink, stove & fridge figure + 70 gal fuel its at about 4240 before passengers.

We went out today with a full fuel tank, 2 adults + 2 kids. Our total combined weight was probably around 450# tipping the scale around 4700#

1st I used the qucksilver 25p prop, at 4000 wot I was only doing 40-42 major prop slip . Out on the water I swapped out to a beat-up Michigan Match 14 1/4 x 21 . That did better same 4000 rpm 39mph on the gps 28% slip.
The one problem I did have is it started cavitation above 4k I trimmed drive down and it really didn't help that much, I could heat the revs jump and feel the prop stop biting. I trimmed the bow up ( lifted the trim tabs) to try to get the drive deeper didn't matter.

Any advice???

I am thinking I might need to add a cavitation plate on the drive.

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

A little added note:

When I'm up on plane & over 30mph on the GPS I usually get the boat almost flat on top of the water I am told it looks like I'm just skinning the water, that the boat is all out and just the prop is in.
Am I using to much trim tab? running with this attitude on the boat, it is when the boat is at its smoothest & fastest. But I did notice that I always have to adjust trim if I have an imbalance is people or load, she will start listing real bad


PS the boat is the Sea Gem listed in my projects, its a Cruisers Inc. Barnagat 220

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

Sorry for leaving out info, its a 22' Cuddy Cabin empty weight is listed as 3600# add the extra cabinet with the sink, stove & fridge figure + 70 gal fuel its at about 4240 before passengers.

We went out today with a full fuel tank, 2 adults + 2 kids. Our total combined weight was probably around 450# tipping the scale around 4700#

1st I used the qucksilver 25p prop, at 4000 wot I was only doing 40-42 major prop slip . Out on the water I swapped out to a beat-up Michigan Match 14 1/4 x 21 . That did better same 4000 rpm 39mph on the gps 28% slip.
The one problem I did have is it started cavitation above 4k I trimmed drive down and it really didn't help that much, I could heat the revs jump and feel the prop stop biting. I trimmed the bow up ( lifted the trim tabs) to try to get the drive deeper didn't matter.

Any advice???

I am thinking I might need to add a cavitation plate on the drive.

25@4000
24@4200
23@4400
22@4600
21@4800

Ok then a worn 21 only gets 4000...Is your tach correct
???Somethings afoot...Is this a 350 efi..2v or 4v your "leg gearing" would help..I would think a 22" cuddy should be able to hit 12% slip


Read your thread a bit...did you end up 330hp???? Your leg gearing is very important here..Hope you didnt end up with a 1.98 gearing and 330 horse..

I read it to conclusion..1.47 the 20 you elected should work..but considering how far you have gone and the size of the boat what another 100..

http://boatpropellers.iboats.com/Me...102190&**********=545176720&*******=819838457


But something is not right with the numbers..missing a tach setting is quite common..boat tachs are not the best


Or are you saying the prop blows out above 4000 rpm?

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Hi Tail Gunner,

Thanks for your response

I think the prop is blowing out, that's why I was thinking of a 4 blade. Maybe the boat is too heavy etc...
I double checked the tach with my fox valley meter, sorry to say its right.
I think the engine is putting out 330hp conservatively, probably more. its a 383 stroker flat tops, fully proted heads comp cams gee 252- 262 I forget but it was an extreme marine the RPM range is 100-5000 The origininal drive was a 1.65 till I blew it up, now it has a new SEI 1.47 For fuel it has a Rochester quad.

With the 21p prop it will pin you to your seat when I goose it

I am only running her up to 4k because of the cavitation or venting problem. With the 21p it has a lot more to go, I am only at 3/4 throttle if that. With the 25p 4 k is about all it will go there is some more throttle but that 39-40mph seems to be the magic # where everything goes to heck

The 21p prop starts blowing out at 4000 no matter what I do. I don't know if its waves messing with me, today the sea was calm, trimmed perfect boat was running flat above the water @ 3500. I gave her a little more juice, as I hit 4k I heard the rpm start running away I could feel it loose its bite, if that makes sense,almost like I hit a speed governor, which I don't have. I dropped the drive in a little further figuring it was lifting the boat a little more, still I was loosing speed and the revs where coming up. I dropped the drive all the way down to the point I should have been plowing working the throttle not to blow anything up.

I did this at least 3 times, same results get the boat running flat, start bringing her throttle up, start loosing it

I didn't order the new prop yet although I wanted it before the weekend. but as you said its only $100 I might just order it tonight/tomorrow to give me a new starting point. the 25p I know is to large, the 21 I have is beat to heck.

I am going back out after hurricane Ralf passes tomorrow/friday, I will try to get a good run video-taped maybe that will help with what is going on

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

Your having some major issues..I looked at your transom leg setup and it looked ok..Could you post a pic with the dive in a straight up and down position..something that shows the height of the cav plate in relation to the hull and one that shows the prop height again in relationship to the bottokm of the hull...last but not least how far are those trim tabs from the drive....10..12...14...18 inches etc..

You say she rock's @ speed with peps aboard..On a 22' boat doing 30 and a rocking left to right is very odd...

Maybe get Bondo or Don involved..It really sounds like your drive is to high...That rocking.. ohh well I like the engine build i went with a 266 cam really changes the motor at the top

Those pics seem clear but something that shows the cav plate in a straight line to the hull..The prop tip should be at least in line with the hulls bottom or below a " or so

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Ok then a worn 21 only gets 4000...Is your tach correct
???Somethings afoot...Is this a 350 efi..2v or 4v your "leg gearing" would help..I would think a 22" cuddy should be able to hit 12% slip

But something is not right with the numbers..missing a tach setting is quite common..boat tachs are not the best


Or are you saying the prop blows out above 4000 rpm?

I know my slip numbers are off the charts when I dropped down to the 21 the slip dropped too but was still unacceptable

I thought maybe the hull configuration at higher speeds????
The original boat was shipped with a 305 and a 16p prop, 12% at 5k and a 16p gives you 41mph but I talked to cruiser inc and they said they also used the same hull with BBC 454's with 23p , set them up for 65mph etc.. I was told not to worry, it was more than capable can and has done it for years

EDIT- just saw your post, looking for pics now

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

I know my slip numbers are off the charts when I dropped down to the 21 the slip dropped too but was still unacceptable

I thought maybe the hull configuration at higher speeds????
The original boat was shipped with a 305 and a 16p prop, 12% at 5k and a 16p gives you 41mph but I talked to cruiser inc and they said they also used the same hull with BBC 454's with 23p , set them up for 65mph etc.. I was told not to worry, it was more than capable can and has done it for years

EDIT- just saw your post, looking for pics now

Am i wrong but your hittting some kind of wall at 39 mph and the props blow..Or 4000 rpm..That should not happen

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Here is a pic I took today of the leg

here is a pic showing the chine and hull configuration
I am attributing the listing on weight distribution because when I am alone I never have that problem

It might sound weird to hear and it is for me to say for fear of sounding nuts but I was told the boat when I have her running flat on plane looks like its all out of the water just skimming across the top. and as nuts as it sounds for a 4000# + boat that's exactly how it feels, and any little weight change tips the apple cart.

The transom on the boat was solid, I didn't have to replace it so I didn't mess with the height

OK I went out and took some measurements, the cavitation plate looks like it is about 3" above the keel. The bottom gimbal housing bolts@ the transom are 6" up from the keel. My trim tabs measuring on the same angle of the hull are 23" to the inboard side of the tab, 41 to the outside
Its dark out so thats the closest I could get for measurements

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Am i wrong but your hittting some kind of wall at 39 mph and the props blow..Or 4000 rpm..That should not happen

That is exactly what seems to be happening . Sounds strange but it happens with either prop the 21 or 25. the 25 is a bear and I have to nurse it to get there but the end result is still the same. I am using a GPS for a speedometer so its not even like the pedo tube is getting messed up. The 21 is like cracking a whip all getup and go until I hit 4k

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

Well i am by no means a expert here but if your cav plate is 3" above the bottom of the hull that should mean your prop tips are above the hull and then your experiencing blow out @ 39 some stability issues...Better go check in the I/O section in regards to a drive height issue..

Hmm you seem quite handy...Maybe you could come up with a setback plate......

I just went and measured mine..Cav plate is 1.75" above the hull and the wellcraft really comes up out of the water..That is it rides very high

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Thanks again for all your help

I measured it in the dark I can be off its hard to sight the ruler to the cavitation plate when you can barely see :redface: , I think I put the drive all the way down when I dropped the boat in my yard but not to sure.
I quickly searched the alpha manual #6 and the engine manual #3 with my wife yelling for the laptop and didn't find the diagram. I will look in the am when she is sleeping and check my measurements look in the manual and find that darn keyhole drawing for the transom assembly etc lol.

well time to let the wife play frontierville I'll post more accurate findings & pics in the AM

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

WOW was I off on my measurements!!! Things look much better in the light of day, guess that's what I get for trying to feel my way through it in the dark. the drive was not all the way down last night and I was trying to eyeball it instead of using a straight edge :redface:

Here is a pic

The bottom of the cavitation plate is only about 1/8 inch above the keel

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

I found a video of her up on plane just below the braking point showing the wake it leaves behind if that helps any

Click on image to play


Here is another one, ignore the screaming children, they were having a blast lol

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

Well....Ok high speed prop slip.....hubs are slipping take a grease pen mark a line from the center bolt to the prop if that line moves..spun hub...Contamination on the bottom of the hull causing extreme drag..find a highly active chemical bath and clean the hull bottom...Mechanical slipping somewhere in the power train...coupler etc..

Sorry but if your leg is at its correct height why your cavitating at 40 dunno what to say..Id say spun hubs..Two back to back is hard to swallow but check it out...I see there old props and the motor is a tourqe monster..Ill be watching this thread..

Hmm heres a great buy on a great prop its made just for your app a 20p will be two small for that boat motor combo

http://boatpropellers.iboats.com/Me...352997&**********=832455214&*******=728959602

 

[HVAC Cruiser]

Re: 21 or 20p 4 blade

Well....Ok high speed prop slip.....hubs are slipping take a grease pen mark a line from the center bolt to the prop if that line moves..spun hub...Contamination on the bottom of the hull causing extreme drag..find a highly active chemical bath and clean the hull bottom...Mechanical slipping somewhere in the power train...coupler etc..

Sorry but if your leg is at its correct height why your cavitating at 40 dunno what to say..Id say spun hubs..Two back to back is hard to swallow but check it out...I see there old props and the motor is a tourqe monster..Ill be watching this thread..

Hmm heres a great buy on a great prop its made just for your app a 20p will be two small for that boat motor combo

http://boatpropellers.iboats.com/Me...352997&**********=832455214&*******=728959602

I hope its the hub slipping and not the coupler I really don't relish the idea of pulling the engine. Your right, that is a real nice prop a 14 1/2 x 22p would probably be perfect and the price is great, but its a counter rotation.

do you think I should stay with a 3 blade? I was thinking with the weight going to a 4

 

[Tail_Gunner]

Re: 21 or 20p 4 blade

opps...:redface: Sorry good thing it wasnt setup for a volvo or id would have a counter rotation prop on the way...

http://boatpropellers.iboats.com/Me.../9521/?**********=589057736&*******=728959602

Thats really is a WAG....But you have a cam that should not run out of steam at the top and if it does...well eldobrock performer will fix that..Personally i would stay with a 4 blade, your pushing 4000 plus lbs you need blade area and lift that hull looks like a deep v so lift will only aid in planing...

I watched the video and your bow is up and it looks like your just getting on plane....Is that the break point..thats not 39mph or 4000 i hope..If it is you have spun hubs...aka your climbing ontop of the pressure wave and the prop lets loose

Pic 1 your climbing out...is it slipping at all..Is that full throttle??
Pic 2 your on plane...Is the prop now slipping if you gun it a bit?


1.Can you slam the throtte and power to plane with no slip
2.Do you have to ease it to plane or she starts slipping

I am wondering here if your not being kind to your new motor and gently applying power getting you around...masking a spun hub or some issue...You should be able to nail it from and it should respond sharply with that much tourqe say for 20 to 40 no slip what so ever...Then this would all make sense that is it blows at 40 even gently nudging it past that speed creates cav

What would happen if you just pinned the throttle form 0 to 35 would it slip or cavitate????