three blade 28 x 28

WoundUpMarine

Admiral
Lite User
Joined
Jan 1, 2012
Posts
6,242
Likes
4,955
Location
Boothbay, Me
First Name
John
Boat Make
26' Duffy, 23' Seaway, 14' Holland

WoundUpMarine

Admiral
Lite User
Joined
Jan 1, 2012
Posts
6,242
Likes
4,955
Location
Boothbay, Me
First Name
John
Boat Make
26' Duffy, 23' Seaway, 14' Holland

captainlarry84

Rear Admiral
Joined
Sep 13, 2011
Posts
1,295
Likes
239
Location
Freeport NY
Boat Make
KristenFormer Charter Captain
no problem, question for all those smarter than I, I have a 26x30 now, would the 28square work for me?
A 26 X 30 & a 28 X 28 carry the same load. Therefore the propeller will work. Before you invest you need to see if more diameter will give you less slippage. The rule of thumb on DE keel boats is max diameter & pitch for load. Also the rule is 4 bladders with a work better. If your 26 X 30 gives you good performance in a 3 bladed wheel, then I would Yes the 28 X 28 would give you better performance. If it was my rig I would want at 28 X 27 four bladed wheel.
In closing this wheel look very fine. Note that the rear of the hub only has the serial # & most likely the pitch & diameter is stamped between the blades which means that from birth the was a new 28 X 28 wheel.
lastly we need to figure your slippage therefore I need the following:
wheel size
reduction gear
speed at WOT & RPMs
speed at cruise & RPMs
also does your current wheel give you the max rated WOT full load RPMs.
 

oldshell55

Captain
Joined
Sep 27, 2013
Posts
653
Likes
162
Location
new york
Boat Make
BHM36 , 38’ young bros ,
slippage

A 26 X 30 & a 28 X 28 carry the same load. Therefore the propeller will work. Before you invest you need to see if more diameter will give you less slippage. The rule of thumb on DE keel boats is max diameter & pitch for load. Also the rule is 4 bladders with a work better. If your 26 X 30 gives you good performance in a 3 bladed wheel, then I would Yes the 28 X 28 would give you better performance. If it was my rig I would want at 28 X 27 four bladed wheel.
In closing this wheel look very fine. Note that the rear of the hub only has the serial # & most likely the pitch & diameter is stamped between the blades which means that from birth the was a new 28 X 28 wheel.
lastly we need to figure your slippage therefore I need the following:
wheel size
reduction gear
speed at WOT & RPMs
speed at cruise & RPMs
also does your current wheel give you the max rated WOT full load RPMs.

Capt. larry, I have used your past post formula to determine slippage, I come up with a no. but don't know how to translate that into something I can understand. my boat goes along very well full wot rpms dead balls on mfg. . can you clarify the slippage #. thanks
 

captainlarry84

Rear Admiral
Joined
Sep 13, 2011
Posts
1,295
Likes
239
Location
Freeport NY
Boat Make
KristenFormer Charter Captain
A good question yet hard to explain. pitch is what moves you forward...therefore of every inch of pitch & every RPM you boat should move forward by 1". However in DE boats the theory does not hold true because the keel is in the way & blocks 100% water flow. to get better performance you need the larger diameter to grab the water which is blocked by the keel. Therefore if you reduce pitch to get better diameter and grab the good water a larger diameter prop will perform better buy grabbing the good water.
Example if your 26 X 30 give you 70% efficiency with 30% slippage * a 28 X 28 gives you 80% efficiency with 20% slippage you will pick performance even though your pitch is reduced.

I think the photo of the Titanic says it all. Note that even back then they knew. the four bladed horse was behind the keel & the wing motors in clear water the 3 bladders. She did 20 plus knots...which was here swan song on that flat calm night.

CCI11172012_00000.jpg
 

captainlarry84

Rear Admiral
Joined
Sep 13, 2011
Posts
1,295
Likes
239
Location
Freeport NY
Boat Make
KristenFormer Charter Captain
I get back to you :confused: with the numbers I have, thanks

See there you go I guess you understand my logic. So get me the #s & we will figure you out before you spend money and chase a white elephant. Also include you vessel so I have better idea on the bottom.
 

oldshell55

Captain
Joined
Sep 27, 2013
Posts
653
Likes
162
Location
new york
Boat Make
BHM36 , 38’ young bros ,
oldshell

See there you go I guess you understand my logic. So get me the #s & we will figure you out before you spend money and chase a white elephant. Also include you vessel so I have better idea on the bottom.

36 bhm 15,000#, 350hp 2700rpm wot, 2:1, does 19+ wot 26x26 4bld dyna quad

may be some confusion I am not woundupmarine looking at the 3 blade, but couldn't resist the chance to crunch numbers with you since I don't understand the slippage number I came up with,(which I can't find now) or how to convert to "efficiency" I really appreciate your input, thanks
 
Last edited:

WoundUpMarine

Admiral
Lite User
Joined
Jan 1, 2012
Posts
6,242
Likes
4,955
Location
Boothbay, Me
First Name
John
Boat Make
26' Duffy, 23' Seaway, 14' Holland

F/V First Team

Admiral
Joined
Jan 10, 2012
Posts
6,146
Likes
2,482
Location
Narnia
Website
www.otisenterprisesmarine.com
Boat Make
Northern Bay 36 - Modified
When I swapped over to a 28 square my idle speed was marginally slower and top end suffered severely.

Had been running a 26x31 (which had originally been a 26x27 before the hammer got to it). We were trying to slow the boat down around the gear, only took off about .25 mph.

Wish my engine spun 2250! :sad:
 

captainlarry84

Rear Admiral
Joined
Sep 13, 2011
Posts
1,295
Likes
239
Location
Freeport NY
Boat Make
KristenFormer Charter Captain
Hey Larry, here we go
Boat is a 36 Crowley Beal spinning a 26x30 left hand. Engine is rated for 2200 and spins up to 2250. Gear ratio is 1.79 to 1.
WOT is 25kts at 2250
Cruise is 20kts at 1800

Excellent #s you are there. At WOT you are running at 81% efficiency which is excellent
At Cruise of 25 knots you are at 80% efficiency

Therefore you are where you want to be. The odds of picking better that 80% with more diameter & less pitch is a draw, I would stay where you are
 
Top Bottom