dhays
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Hull Shapes----Show us your girl's bottom
- Thread starter Moonstruck
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The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
Quite frankly, she is stunning. Congratulations!
menzies
Guru
Sailor of Fortune
Guru
She sho,nuf purdy!
Nomad Willy
Guru
Three blade props are better unless they are not enough blade area for your power.
menzies
Guru
Hmmm, data?
For screw-cutting through water, in general: Three blades are more efficient than four. Two more efficient than three. One more efficient than two... that is if it could be figured out how to properly balance one blade??
That said: The more blades the easier it is to balance the prop. Also, as I believe Eric mentioned... if three blade circumference can not be made large enough due to space limitations then adding an extra blade (or two extra blades) can solve the problem of ample sq. inch blade surface for required screw-cutting power.
This is general physics... including a bit of unique prop design engineering thrown in!
menzies
Guru
Interesting. There is a lot of information out there that would argue that point - but I want to hear other opinions here as well. It could be that four blades are more optimal on planing hulls that trawlers because of hole shot and speed at lower torque levels.
But willing to learn here.
Lou_tribal
Guru
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Here is my baby's bottom. Poor girl she is freezing her bottom in the snow
Here is my baby's bottom. Poor girl she is freezing her bottom in the snow
Nomad Willy
Guru
menzies,
Number of blades is a matter of propeller loading.
High speed cruisers probably mostly have 4 blade props because they have lots of power. Cruisers need heavily loaded props to go relatively fast and are mostly 4 blade driven. Some RecTrawlers have shallow draft and thus limited dia space for props so need more blades.
Whatever the variables dictate they will lead to the near ideal blade loading for the boat in question. Whatever your boat came with was choosen by the NA to optimize blade loading. Using a prop w more blades will only decrease performance unless the boat has more power than it came with. Many think 4 blade props are better (for whatever reason) but it's fortunate that the performance loss is small.
The MV Content has propellers like my Willy. Definitly not as efficient as the more modern "skewed" blade design props. But reverse thrust is much greater and some say are also smoother. Both Content and my Willy have room for a larger dia prop but have smaller for what ever reason. I think I know why but it's just a personal theory. It has to do w the speed range of top performance using large dia props. The reduced range means the boat only performs really well in a narrow range of loading and speed.
Willy's prop when I was using Pettit Barnacle Buster, a "cold galvanize" light grey coating. Did'nt perform well enough to repeat but it shows the blade shape well. I found another pic that shows the symmetrical blade prop even better. It also shows how whale like the W30 is. A little to excess. It was taken on the tidal grid in SE Alaska.
Number of blades is a matter of propeller loading.
High speed cruisers probably mostly have 4 blade props because they have lots of power. Cruisers need heavily loaded props to go relatively fast and are mostly 4 blade driven. Some RecTrawlers have shallow draft and thus limited dia space for props so need more blades.
Whatever the variables dictate they will lead to the near ideal blade loading for the boat in question. Whatever your boat came with was choosen by the NA to optimize blade loading. Using a prop w more blades will only decrease performance unless the boat has more power than it came with. Many think 4 blade props are better (for whatever reason) but it's fortunate that the performance loss is small.
The MV Content has propellers like my Willy. Definitly not as efficient as the more modern "skewed" blade design props. But reverse thrust is much greater and some say are also smoother. Both Content and my Willy have room for a larger dia prop but have smaller for what ever reason. I think I know why but it's just a personal theory. It has to do w the speed range of top performance using large dia props. The reduced range means the boat only performs really well in a narrow range of loading and speed.
Willy's prop when I was using Pettit Barnacle Buster, a "cold galvanize" light grey coating. Did'nt perform well enough to repeat but it shows the blade shape well. I found another pic that shows the symmetrical blade prop even better. It also shows how whale like the W30 is. A little to excess. It was taken on the tidal grid in SE Alaska.
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markpierce
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Willy, your efficient hull requires no more than provided by a three-bladed propeller. In contrast, the FAT, hull-speed Coot does well with four blades.
MV Content
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- MV Content
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- Fellows & Stewart 58' Pilothouse Cutter
When I bought Content, she had the original White Superior 100s in there. I had to re-power in 2013, and went with Iveco 150s. The prop calculation said I should stick with the originals, 28x23. Original gearbox was 1:2 - new one is 1:2.9. Very economical (1.6 gph@7kts@1200rpm), and handling is great in tight situations. I'm no expert, though!
Indeed economical at 4.4 nmpg!
Did White Superior 100's provide similar, better or worse nmpg, at same speed? And, how many hrs. on those old babies before replacement?
How much run-for-it emergency speed increase at WOT have Iveco 150s afforded you?
Any notable weight difference between the two engine Brands?
As you can tell your beautiful, stately, artistic design boat interests me!
MV Content
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Art,
The old engines were pretty good......used about two gallons@1100RPM, which gave us about 7.5kts. I really couldn't say how many hours, because those meters didn't work when I bought her. However, they were installed in 1930, and lasted 83 years, so they covered some miles!
I reckon I reduced the weight by about a ton, maybe a little more. She'll run for home now at about 14kts, but I've not had her at WOT for more than a minute or two.
Eamonn
The old engines were pretty good......used about two gallons@1100RPM, which gave us about 7.5kts. I really couldn't say how many hours, because those meters didn't work when I bought her. However, they were installed in 1930, and lasted 83 years, so they covered some miles!
I reckon I reduced the weight by about a ton, maybe a little more. She'll run for home now at about 14kts, but I've not had her at WOT for more than a minute or two.
Eamonn
Eamonn
Thanks for replies to questions I ask! The 83 old babies were getting about 3.75 nmpg - still, that's damn good, although not as good as your new ones. Your boat is very efficient. Ton weight reduction is substantial. 14kts - impressive. I also don't keep WOT on any boat for but minute or two... like sea test when purchasing or doing tune up tests and the occasional need to get the heck well away from a potentially dangerous situation. Nice to have ample HP when needed.
What was top speed at WOT with the old engines you replaced? Any where near the 14kts you can get when necessary with the new babies?
Happy "Boat-Love" Daze! - Art
This is interesting....
Walt, TY for providing info!
What is said about 4 blades compared to three makes it sound as though 4 is better than 3 in many if not all ways?? That's news to me, but, good to know... if it's test proven factual.
Sure is different than I was taught as a "marineite" type person working with persons at boat yards when young as well as having an engineer dad who conducted prop tests. And, having read "prop" books. I've a good prop book on the boat I'll delve into next visit and at anchor.
So, makes me wonder: Why, if as this blurb says that 4 blades is in many ways better than 3, wouldn't that make it seem that 5 is better than 4?
I do get pretty darn confused when it comes to intricate details of prop design. Then again so do a lot of engineers. Boat prop design has a bit o' "magic" in the "water-screw" formation there of. From everything I heard, read and learned the less blades on a prop the more efficient it was/is (of course with correct [applicable] blade surface area, placement on hub, edge sharpness/angle, and pitch/twist).
Ah the wonders of "Boat-Life"!
MV Content
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Nomad Willy
Guru
It's the ratio of pitch to diameter that counts and dictates if you've got too many or too few blades. If MV Content had a 30" X 19" prop better performance would probably be had w the 28X23 props. So as Eamonn says the prop calculation proved correct on the Content. A fourth blade would have required a big reduction in pitch to load the four blades correctly. That would mean the resulting prop would be about 28 X 18 .. just a guess. Huge difference in the pitch/dia ratio. Not pushing much water but eating up much power swinging that fourth blade around. If you keep decreasing pitch and adding blades eventially you'll wind up w a flat disk. Could be the same dia but probably will be more dia. All the power of the engine/s will be consumed turning the blades through the water and no thrust created. And of course if you go the other extreme w too little dia and too much pitch eventially you'll get 90 degrees to a feathered prop. Blades aligned w the prop shaft. With a certian blade size and dia all the power will be required to reach rated rpm and absolutely no thrust will be generated.
So either extreme will consume all the power and produce no thrust. So for every blade dia and area and blade design and speed through the water there is a perfect or better put optimal pitch and dia. The number of blades is almost meaningless but if you can't get enough dia to be in the optimal zone w 3 blades you then need four. So usually the factor that dictates 3 or 4 blades is swinging room for the propeller .. the maximum dia that is practical. There is a small range or zone that either 3 or 4 blades will produce the same efficiency. Then it matters not if you have three or four blades. The four blade just costs more money. So the basic rule of thumb is "three is best unless you need four".
And this "hole shot" talk has no place on TF. On outboards four blades are used to get blade area. Just like trawlers but in the case of OB's much more limited space is available.
So either extreme will consume all the power and produce no thrust. So for every blade dia and area and blade design and speed through the water there is a perfect or better put optimal pitch and dia. The number of blades is almost meaningless but if you can't get enough dia to be in the optimal zone w 3 blades you then need four. So usually the factor that dictates 3 or 4 blades is swinging room for the propeller .. the maximum dia that is practical. There is a small range or zone that either 3 or 4 blades will produce the same efficiency. Then it matters not if you have three or four blades. The four blade just costs more money. So the basic rule of thumb is "three is best unless you need four".
And this "hole shot" talk has no place on TF. On outboards four blades are used to get blade area. Just like trawlers but in the case of OB's much more limited space is available.
Nomad Willy
Guru
I started a new tread "Pitch Dia. Ratios for Props".
Back to bottoms.
Back to bottoms.
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boathealer
Guru
I see hull #1 is in the water and undergoing trials. Videos from just yesterday online now. Pretty neat boat.
cardude01
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Sea trial video:
https://youtu.be/kO-TEHNBr3o
Sure hope there is a door for the transom. With the cabin door at deck level it seems easy to get pooped and have water in the cabin.
Spiffy looking boat IMO.
https://youtu.be/kO-TEHNBr3o
Sure hope there is a door for the transom. With the cabin door at deck level it seems easy to get pooped and have water in the cabin.
Spiffy looking boat IMO.
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Digging big hole in water w/ quite the wake. Fuel use stats??
Nomad Willy
Guru
I'm pleasantly supprised at the Sandpiper. Looks like she's going about 9 knots and riding very level for that speed. The bow wave waves are breaking. There may be a reason they show her at only that speed. I was thinking at over 7 knots fwd visability would be limited w the far aft wheelhouse. Would like to see more. The aft wheel house is an ideal location given a light boat and fairly flat/shallow V hull. Perhaps the boat has a hooked stern. Haven't seen hull pics.
long-cours.62
Guru
Prop 4 blades vs 3 blades
One sample of choice between 4 and 3 blades
For consumption our best compromise is at 7 kts for just under 1,5 usg per hour
And our last trial 120 nm with a customer @ 8,5 kts 3,28 usg per hour
At 7 kts it could be better if we had not the "brake" of the unused 27" 4 blades propeller
One sample of choice between 4 and 3 blades
For consumption our best compromise is at 7 kts for just under 1,5 usg per hour
And our last trial 120 nm with a customer @ 8,5 kts 3,28 usg per hour
At 7 kts it could be better if we had not the "brake" of the unused 27" 4 blades propeller
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Donna
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