Fuel Efficiency: Smooth Plate Hull vs Sheet w/Formed Ribs
-
- WON Super Star Donator '08, '09, '10, '11
- Posts: 638
- Joined: Sat Mar 15, 2008 1:07 pm
- 16
- Location: So. Calif.
Fuel Efficiency: Smooth Plate Hull vs Sheet w/Formed Ribs
Are aluminum hulls that are built using smooth plate alloy more fuel efficient than hulls built using thinner sheet that form ribs in the surface to increase it's stiffness?
The thinner sheet (tinnies) with formed in ribbing are lighter, but do they have more drag while at cruise speeds compared to hulls that are smooth?
Plate alloy hulls would be heavier, but will the smooth surface make them more efficient over a lighter hull with surface ribs with similar configurations?
Thanks for any replies
PS: Be easy on my rig. Shes not a spring chicken anymore! (19 yrs. old)
The thinner sheet (tinnies) with formed in ribbing are lighter, but do they have more drag while at cruise speeds compared to hulls that are smooth?
Plate alloy hulls would be heavier, but will the smooth surface make them more efficient over a lighter hull with surface ribs with similar configurations?
Thanks for any replies
PS: Be easy on my rig. Shes not a spring chicken anymore! (19 yrs. old)
1989 22' Walkaround Cuddy Bayrunner
2001 115 Merc. 4 stroke/1988 9.9 Yamaha 4 stroke kicker
- Jay Perrotta
- Sponsor/Donator
- Posts: 376
- Joined: Sat Jan 05, 2008 4:27 am
- 16
- Your location: Freeport, Maine, USA
- Location: Freeport, Maine, USA
I'm not sure.
The ribs are definitely "drag" but may also have the effect of breaking surface tension.
The water passing over the bottom is both going fore to aft and also moving from center to edge.
In breaking the movement from center to edge and addding air you may well be reducing drag. Hard to tell without testing - would just be an opinion!
I like your boat!
The ribs are definitely "drag" but may also have the effect of breaking surface tension.
The water passing over the bottom is both going fore to aft and also moving from center to edge.
In breaking the movement from center to edge and addding air you may well be reducing drag. Hard to tell without testing - would just be an opinion!
I like your boat!
Jay Perrotta
-
- Posts: 199
- Joined: Tue Jan 08, 2008 11:53 pm
- 16
- Location: Mexico
Strakes catching water and bubbles forced up from the keel theoreticly create more lift and a thicker bubble or air layer between the hull and the moving water reducing laminar flow friction.
But the ribs do increase the wetted surface area so depending on the amount, this could be a toss up.
The primary benifit of the ribs also allow for thinner material which cuts weight, widens the centers for fewr stringers, which save on material and labor.
I know a couple of guys who have twin 50 hp motors on a 22' Baja and that they burn very little gas going offshore, but the deadrise on their hull is also prettly flat at the transom, so a head to head comparision against a plate alloy boat is not to comparable as they get a pretty harsh ride in the chop.
But the ribs do increase the wetted surface area so depending on the amount, this could be a toss up.
The primary benifit of the ribs also allow for thinner material which cuts weight, widens the centers for fewr stringers, which save on material and labor.
I know a couple of guys who have twin 50 hp motors on a 22' Baja and that they burn very little gas going offshore, but the deadrise on their hull is also prettly flat at the transom, so a head to head comparision against a plate alloy boat is not to comparable as they get a pretty harsh ride in the chop.
- JETTYWOLF
- Contributor/donator/Location Nazi
- Posts: 6074
- Joined: Sun Jan 06, 2008 9:11 pm
- 16
- Your location: JACKSONVILLE FL USA
- Location: Tree-hugger, USA...they call it FLA.
Just a shot in the dark, but since the whole boat is one rib after another, it would seem to me that the reason is strengthening period.
If the ride gets better over the bottom pieces because of it, or the mileage is better, is just a benefit of the design and materials used to create a light weight boat with stronger stiffened pieces, out of neccesity.
But what the hell do I know...I'm over the top happy with my my mileage.
If the ride gets better over the bottom pieces because of it, or the mileage is better, is just a benefit of the design and materials used to create a light weight boat with stronger stiffened pieces, out of neccesity.
But what the hell do I know...I'm over the top happy with my my mileage.
-
- Donator '09 '10
- Posts: 510
- Joined: Wed Jan 09, 2008 9:27 pm
- 16
- Your location: NY
- Location: Montauk, NY
In2deep,
Looking at your bottom chines makes me think that the rounded edged to the keel side would tend to hold more air bubbles than most hard chines. That said, it should help your speed and economy. But I don't think for a boat that size with its weight it really matters a whole lot. You gotta be very economical, so if you had hard chines instead of rounded it may be less effective. Cool looking little fisherman you have there. Mty
Looking at your bottom chines makes me think that the rounded edged to the keel side would tend to hold more air bubbles than most hard chines. That said, it should help your speed and economy. But I don't think for a boat that size with its weight it really matters a whole lot. You gotta be very economical, so if you had hard chines instead of rounded it may be less effective. Cool looking little fisherman you have there. Mty
"IRONWOODTUNA" the Alloy Sportfisherman Battleship!
-
- WON Super Star Donator '08, '09, '10, '11
- Posts: 638
- Joined: Sat Mar 15, 2008 1:07 pm
- 16
- Location: So. Calif.
Thanks for your thoughts and opinions.
This was something that I've always wondered about and never had anyone to ask it to.
I guess what prompted me to ask was the mileage figures that Welder had posted for his rig. Quite impressive if those are average figures and not just "one time I got "
I'm getting 3.0-3.250 nautical MPG's per trip readout on the GPS.
Been doing 42-45 mi. trips on 13-15 gallons.
Usually cruise at 19-20 knots@ 4100-4400 RPM
It probably doesn't help that my rig is not exactly aerodynamic with the hard top and full enclosure, kicker and two extra fuel tanks under the gunnels.
I can't complain because I used to get under 2 MPG's while running a 130HP Yamaha 2-stroke with the smell and noise
This was something that I've always wondered about and never had anyone to ask it to.
I guess what prompted me to ask was the mileage figures that Welder had posted for his rig. Quite impressive if those are average figures and not just "one time I got "
I'm getting 3.0-3.250 nautical MPG's per trip readout on the GPS.
Been doing 42-45 mi. trips on 13-15 gallons.
Usually cruise at 19-20 knots@ 4100-4400 RPM
It probably doesn't help that my rig is not exactly aerodynamic with the hard top and full enclosure, kicker and two extra fuel tanks under the gunnels.
I can't complain because I used to get under 2 MPG's while running a 130HP Yamaha 2-stroke with the smell and noise
1989 22' Walkaround Cuddy Bayrunner
2001 115 Merc. 4 stroke/1988 9.9 Yamaha 4 stroke kicker
-
- Posts: 199
- Joined: Tue Jan 08, 2008 11:53 pm
- 16
- Location: Mexico
Your fuel economy should be a lot better than that (on a 22 footer??) IMO. Maybe as much as 2x better.
I am going to make some comments that I hope you will take as helpfull observations.
From the pictures of the underside of your bow it would appear that there are some large dents on the port side that will catch a lot of water. These spoons need to be pushed or pulled out to recreate low drag planning surfaces.
Baja runners are also rough in a head sea chop, so if you are trimming down the bow to compensate this will drastically cut your mileage in any hull and place the bow dents into the water will afftect you even more, like a plow or a brake. You might also consider a fine sand and sealer if her old bottom is getting rougher than slippery.
To run more in a trimmed up position to get more speed at the same rpm consider adding some lenco trim tabs to extend your footprint and get a pair of spring-shock absorber seat to soften the ride. These go for about $110 each.
http://www.tractorpartsinc.com/universa ... 11_ctg.htm
I would guess that weight and motor height and perhaps a different prop might help.
Please consider a membership to sea tow in San Diego so that you can lose the kicker and all the extra gas you are carrying. Plus the boat will ride nice and level without the kicker on one side.
Cut your gear weight down to the essential, especially in the forward cabin. You may be running the motor at an extreme uneffecient angler to trim up if there is too much weight forward, and cabins allways collect more "essential items" over time. So here we are talking toal weight and how you have her balanced with that weight.
Use wet burlap bags instead of a lot of ice to cool your fish, and only put up the forward eisenglass windshield when you need it. The side panels shouldn't affect your speed near as much as the front one.
Blast me if I am wrong, I'm real thick skinned.
BTW, I really like your rig.
I am going to make some comments that I hope you will take as helpfull observations.
From the pictures of the underside of your bow it would appear that there are some large dents on the port side that will catch a lot of water. These spoons need to be pushed or pulled out to recreate low drag planning surfaces.
Baja runners are also rough in a head sea chop, so if you are trimming down the bow to compensate this will drastically cut your mileage in any hull and place the bow dents into the water will afftect you even more, like a plow or a brake. You might also consider a fine sand and sealer if her old bottom is getting rougher than slippery.
To run more in a trimmed up position to get more speed at the same rpm consider adding some lenco trim tabs to extend your footprint and get a pair of spring-shock absorber seat to soften the ride. These go for about $110 each.
http://www.tractorpartsinc.com/universa ... 11_ctg.htm
I would guess that weight and motor height and perhaps a different prop might help.
Please consider a membership to sea tow in San Diego so that you can lose the kicker and all the extra gas you are carrying. Plus the boat will ride nice and level without the kicker on one side.
Cut your gear weight down to the essential, especially in the forward cabin. You may be running the motor at an extreme uneffecient angler to trim up if there is too much weight forward, and cabins allways collect more "essential items" over time. So here we are talking toal weight and how you have her balanced with that weight.
Use wet burlap bags instead of a lot of ice to cool your fish, and only put up the forward eisenglass windshield when you need it. The side panels shouldn't affect your speed near as much as the front one.
Blast me if I am wrong, I'm real thick skinned.
BTW, I really like your rig.
Last edited by Bullshipper on Wed May 14, 2008 6:22 am, edited 3 times in total.
-
- WON Super Star Donator '08, '09, '10, '11
- Posts: 638
- Joined: Sat Mar 15, 2008 1:07 pm
- 16
- Location: So. Calif.
Thanks for the reply Bullshipper.
You have a sharp eye spotting the dents on the port bow. Unfortunately, these larger Bayrunners of this vintage don't take kindly to pounding them too hard as you can see.
I've tried to pound them out from the inside but didn't have success so I just left it as is.
I already have Bennett trim tabs that I make a lot of use of to trim the bow down when running up swell and not pound.
I have a Vessel Assist membership and would never have a boat without a kicker on it for safety reasons and I use it often to slow troll for halibut and trout in the freshwater. The weight of the kicker is off-set with the dual batteries on the opposite side
I like to keep my catch cold with frozen two liter bottles and don't carry a lot of weight ice wise.
You are probably right in regards to the forward eisenglass, But I've become accustomed to not having the wind hitting my face so it will stay up.
I do appreciate the advice you have given and will take it into consideration.
I should experiment with some other props. Right now I'm running a 15" pitch and I can get 5400rpm running fairly light.
Next choice would be a 13" pitch and that should get 5800rpm.
Could that make much of a difference?
Glad you like it. I enjoy it very much myself. :D
Welder
I have never weighed it, but it probably weighs more than most other 22' Bayrunners out there by the way it tows.
Scott
You have a sharp eye spotting the dents on the port bow. Unfortunately, these larger Bayrunners of this vintage don't take kindly to pounding them too hard as you can see.
I've tried to pound them out from the inside but didn't have success so I just left it as is.
I already have Bennett trim tabs that I make a lot of use of to trim the bow down when running up swell and not pound.
I have a Vessel Assist membership and would never have a boat without a kicker on it for safety reasons and I use it often to slow troll for halibut and trout in the freshwater. The weight of the kicker is off-set with the dual batteries on the opposite side
I like to keep my catch cold with frozen two liter bottles and don't carry a lot of weight ice wise.
You are probably right in regards to the forward eisenglass, But I've become accustomed to not having the wind hitting my face so it will stay up.
I do appreciate the advice you have given and will take it into consideration.
I should experiment with some other props. Right now I'm running a 15" pitch and I can get 5400rpm running fairly light.
Next choice would be a 13" pitch and that should get 5800rpm.
Could that make much of a difference?
Glad you like it. I enjoy it very much myself. :D
Welder
I have never weighed it, but it probably weighs more than most other 22' Bayrunners out there by the way it tows.
Scott
1989 22' Walkaround Cuddy Bayrunner
2001 115 Merc. 4 stroke/1988 9.9 Yamaha 4 stroke kicker
Hi Scott,
The second edition of Stephen Pollard's book "Boatbuilding with Aluminum" states that strakes are not for additional lift but rather add bottom stiffness and reduce drag by knocking down spray. I'm inclined to think that the additional surface area created by the formed-in strakes on your vessel would result in little drag penalty vs. the upside of lighter weight with greater stiffness for a given bottom sheet thickness. Perhaps these longitudinals help with tracking as well.
The second edition of Stephen Pollard's book "Boatbuilding with Aluminum" states that strakes are not for additional lift but rather add bottom stiffness and reduce drag by knocking down spray. I'm inclined to think that the additional surface area created by the formed-in strakes on your vessel would result in little drag penalty vs. the upside of lighter weight with greater stiffness for a given bottom sheet thickness. Perhaps these longitudinals help with tracking as well.
Re: Fuel Efficiency: Smooth Plate Hull vs Sheet w/Formed Ribs
[quote="IN2DEEP"]Are aluminum hulls that are built using smooth plate alloy more fuel efficient than hulls built using thinner sheet that form ribs in the surface to increase it's stiffness?
The thinner sheet (tinnies) with formed in ribbing are lighter, but do they have more drag while at cruise speeds compared to hulls that are smooth?
Plate alloy hulls would be heavier, but will the smooth surface make them more efficient over a lighter hull with surface ribs with similar configurations?
Thanks for any replies
PS: Be easy on my rig. Shes not a spring chicken anymore! (19 yrs. old)
it actually a nice protection for the boat as you installed it, but for me i can suggest if you want to add paint
_________________
aluminum plate
The thinner sheet (tinnies) with formed in ribbing are lighter, but do they have more drag while at cruise speeds compared to hulls that are smooth?
Plate alloy hulls would be heavier, but will the smooth surface make them more efficient over a lighter hull with surface ribs with similar configurations?
Thanks for any replies
PS: Be easy on my rig. Shes not a spring chicken anymore! (19 yrs. old)
it actually a nice protection for the boat as you installed it, but for me i can suggest if you want to add paint
_________________
aluminum plate
Re: Fuel Efficiency: Smooth Plate Hull vs Sheet w/Formed Ribs
You better watch out, or they might take your worm! I have a 21' Bayrunner Baja with a custom pilot house. Loaded for Albacore it weighs in at about 3300#. With my mid 90's Johnson 90, I get an average of about 2 1/2 to 3 mpg. That includes a 50 mile run out, 4 hrs of trolling, and a 50 mile run back usually in less that ideal conditions. I cruise at about 20 mph on the way out with FAC conditions. Usually come back in at about 12 to 15 mph in chop in the PM.