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Author Topic:   15-foot Top Speed

runpasthefence posted 07-21-2005 02:05 AM ET (US)
This Spring I rigged a 2005 90hp Yamaha on my recently acquired 1985 15' sport. I was unable to get an initial top speed reading with a fairly bare boat because I neither had a speedometer nor a GPS.
Well, that's changed. I now have a GPS to read speed, but I also have added a false floor that consists of 3/4" plywood, three braces, glass, gelcoat, etc. I've also addend two backrests, bow cushion (rather large), bench cushion, cd player, 2 6.5" speakers, ski pole (tripod style), and probable a few others.
My issue is, my boat runs 48.5 mph WOT with OR without all of the accessories. I am limited by a severe chine walk at this speed. It seems that no matter how much weight I remove, I still maintain the same speed. I could go for a higher pitched prop, but the chine-walk will still be there in the upper 40's Therefore, this tells me that my 15'refuses to go over 48-49 mph with it's current hull design. Maybe I'm wrong.
I've heard of people with 90hp on 15's that run in the mid 50mph zone with no hull mods. So what am I doing wrong? Is this just an exageration? It definately does FEEL like 55..maybe 65.
Regardless, this winter im glassing in an Allison-Craft like pad on the bottom of my whaler to eliminate "the walk". I plan to compliment this with a hydrolic jack plate, low water pick up, amongst other non-warrantee-voiding goodies. Just looking for opinions/experiences. Thanks.
Mick
Peter posted 07-21-2005 08:03 AM ET (US)
Using the performance prediction formula (see www.continuouswave.com/whaler/reference/prop2.html ) to estimate top speed for the classic 15 hull using 180 as the hull constant for a standard configuration (I've found 180 to be the most accurate), a top speed of about 49 MPH is what is predicted. Anybody claiming to achieve higher than that has either modified the motor to achieve more HP or made other modifications such as using a jack plate to raise the height of the motor which thereby changes the hull constant to a higher number. A hull constant of 200 would be necessary to achieve close to 55 MPH with a 90 HP motor.
Peter posted 07-21-2005 08:04 AM ET (US)
I should have added that without modifications to change the hull constant, 115 HP would be required to achieve 55 MPH.
Buckda posted 07-21-2005 10:16 AM ET (US)
I have to ask: Are you racing this boat? Trying to keep up with your buddy's Ranger?
It seems like quite a bit of expense for a 4-5 MPH increase; but then again, you're already overpowered by more than 20%...
Just curious. To think that I was nervous at WOT in my 15 with 70 HP at 43 MPH!!!
Teak Oil posted 07-21-2005 10:17 AM ET (US)
Before you get out the grinder and sander I would try raising the motor a hole or two.
Also go for the jackplate and maybe even try a doel fin, its cheap and just might stabilize things.
As you know a round bottom is not the best for top speed. Be sure to have a safety lanyard and life jacket ready for those high speed runs, you are going faster than Whaler ever intended on that hull
runpasthefence posted 07-21-2005 10:56 AM ET (US)
No racing, other than some VERY amateur stuff done on sunday evenings. As for why, well, I just like the speed. I also kind of like the idea of having the 15' that everyone talks about around the area. As for the money, it really isn't so bad. I get all of my parts at cost and do all of my own work (perks of working at a marine maintenance shop).
Teak, the maximum vertical adjustment has already been done...short of a jack-plate. I'd like to stay away from a dole-fin, but I see where you're coming from. Probably going to add some good goggles to that safety list, the boat is already a tear-jerker.
Peter posted 07-21-2005 11:24 AM ET (US)
How about a helmet too! ;)
scaleplane posted 07-21-2005 12:45 PM ET (US)
Gotta say, 30 mph WOT with my 40HP Johnson is fast enough for me on my 15'. In fact, I usually choose to cruise around 20-22 very comfortably. Guess I'm getting old!
runpasthefence posted 07-21-2005 07:46 PM ET (US)
keep in mind, this is also a pleasure/ski boat. hence the forth coming jackplate. i dont want to permanently mount my motor that shallow. yeah i know im trying to accomplish a lot of this little boat, but what's a whaler nut supposed to do?
Binkie posted 07-22-2005 07:30 AM ET (US)
You just need more motor.Try a 2.4 Merc race motor. You`ll need a jack plate, but you will have to run the motor lower than the transom, due to the short racing lower unit, but the lower motor will give you more stability. The rounded bottom will make for a hairy ride, A pad would help, if you can get it right. Going fast is fun, your only limited by the "scared" factor.
runpasthefence posted 07-22-2005 02:15 PM ET (US)
I think the 2.4 is around 285hp? I know the 2.5 is 300, and close to 400lbs. Call me chicken, but 400% over the max-rated horespower seems a little overkill. We've got a couple of Yamaha 115s that I might try out after everything else is buttoned up.
jimh posted 07-24-2005 09:15 AM ET (US)
Administrative post
dnh posted 07-24-2005 05:08 PM ET (US)
runpasthefence, do you have any photos of your boat? I have a 1986 Sport and would like to see I photo of it with the 2005 90 on it...
runpasthefence posted 07-25-2005 02:36 AM ET (US)
No problem. I'll probably update this with more detail and update it with progress over the winter. http://photobucket.com/albums/v611/yeahtoast02/project%20Ambelina/
dnh posted 07-25-2005 08:56 AM ET (US)
runpastthefence,
I just noticed you are in Charleston also. That's a nice picture of your boat with the keys in the background. I was out in mine yesterday in Beresford Creek, etc., perhaps I will see you out sometime.
I'd actually like to get together some time if I get serious on the new engine and give yours a test run.
Your boat looks pretty similar to mine but nicer.
http://photobucket.com/albums/v672/dnh2
Barefoot posted 07-25-2005 02:40 PM ET (US)
Growing up I could get 47 out of my 15 with a 70HP on it. The boat's hull speed will not let it go much faster. Go buy a hydro and in the mean time be carefull not to blow the 15 whaler over.
BOB KEMMLER JR posted 07-25-2005 03:50 PM ET (US)
Mick-I'm planning on doing a lot of those same mods on a 15 Mischief with 115+hp merc tower.i think the mischief might have a slight edge over the reg sports because of the added weight of the cap and the added weight forward(plus they just look faster lol) due to the drivers position.Don't forget the steering wheel mounted trim unit and hot foot throttle.I'm also thinking of adding a 20 gallon or so belly tank under the foredeck area to get a little more weight up front.good luck and keep it right side up.
runpasthefence posted 07-25-2005 05:40 PM ET (US)
DNH, anytime you want to go for a run just email me at yeahtoast02@yahoo.com, I'll be back at The Citadel the 21st, but weekends are still usually free.
Bob,I would love to see that boat. I wasn't aware the Mischief even existed previous to this winter. Definately a neat boat. It probably is better suited for what we're trying to achieve in speed, but I've never seen that proven. It would definately be interesting to compare. Im in the same situation with my fuel tank as well, but since the bow of my boat is much less protected and probably walked on more often...I'm trying to find a Pate or possibly a tempo to fit under my false floor. Im hoping to negate the added weight of that upcoming jack-plate. I am jealous of your 115 though. I mentioned earlier that I was going to bolt up a V4 Yam 115 for a weekend or so, but i think I've come to the conclusion that I'm just going to void my warranty to get another 20-30 horsepressure out of the three cylinder. Be sure to keep me updated, I'd love to see how things turn out.
myakka posted 07-25-2005 09:05 PM ET (US)
Bob
I've been away for a while... YOU GOT A MISCHIF?
Mike
where2 posted 07-25-2005 09:45 PM ET (US)
If I could just find the racing lower unit off an OMC Sprint 75 (used on racing hydroplanes), and the right prop, I'm sure I could top that 47mph number Barefoot has...
dnh posted 07-25-2005 09:55 PM ET (US)
I do not believe the posts about there being a "top speed" of 48mph, etc. on the hull. I have no factual basis other than to say it doesn't seem to make sense.
If you get the boat on an absolutely glass surface with a 115 on it, it sure as heck ought to go faster than the same boat with a 70. Maybe you got to put a weight in the front, etc. Maybe not.
I have seen game warden 15s with 115xp Evinrudes on them. Ive seen two of these, old heavy 4cyl OMC engines. If it didnt make them run any faster than the 70, why would they be on there? It wasnt for towing or torque.
If the boat is loaded carefully, the water is flat, and its trimmed correctly, it won't walk.
BOB KEMMLER JR posted 07-25-2005 09:59 PM ET (US)
Not yet Mike,but i may be taking a road trip to Mn to get one very soon.I have my eye on a few 115-150 Merc Towers too.My wife is planning on upping my life insurance policy as soon as the boats in the driveway hehe

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Author	Topic: 15-foot Top Speed
runpasthefence	posted 07-21-2005 02:05 AM ET (US) This Spring I rigged a 2005 90hp Yamaha on my recently acquired 1985 15' sport. I was unable to get an initial top speed reading with a fairly bare boat because I neither had a speedometer nor a GPS. Well, that's changed. I now have a GPS to read speed, but I also have added a false floor that consists of 3/4" plywood, three braces, glass, gelcoat, etc. I've also addend two backrests, bow cushion (rather large), bench cushion, cd player, 2 6.5" speakers, ski pole (tripod style), and probable a few others. My issue is, my boat runs 48.5 mph WOT with OR without all of the accessories. I am limited by a severe chine walk at this speed. It seems that no matter how much weight I remove, I still maintain the same speed. I could go for a higher pitched prop, but the chine-walk will still be there in the upper 40's Therefore, this tells me that my 15'refuses to go over 48-49 mph with it's current hull design. Maybe I'm wrong. I've heard of people with 90hp on 15's that run in the mid 50mph zone with no hull mods. So what am I doing wrong? Is this just an exageration? It definately does FEEL like 55..maybe 65. Regardless, this winter im glassing in an Allison-Craft like pad on the bottom of my whaler to eliminate "the walk". I plan to compliment this with a hydrolic jack plate, low water pick up, amongst other non-warrantee-voiding goodies. Just looking for opinions/experiences. Thanks. Mick
Peter	posted 07-21-2005 08:03 AM ET (US) Using the performance prediction formula (see www.continuouswave.com/whaler/reference/prop2.html ) to estimate top speed for the classic 15 hull using 180 as the hull constant for a standard configuration (I've found 180 to be the most accurate), a top speed of about 49 MPH is what is predicted. Anybody claiming to achieve higher than that has either modified the motor to achieve more HP or made other modifications such as using a jack plate to raise the height of the motor which thereby changes the hull constant to a higher number. A hull constant of 200 would be necessary to achieve close to 55 MPH with a 90 HP motor.
Peter	posted 07-21-2005 08:04 AM ET (US) I should have added that without modifications to change the hull constant, 115 HP would be required to achieve 55 MPH.
Buckda	posted 07-21-2005 10:16 AM ET (US) I have to ask: Are you racing this boat? Trying to keep up with your buddy's Ranger? It seems like quite a bit of expense for a 4-5 MPH increase; but then again, you're already overpowered by more than 20%... Just curious. To think that I was nervous at WOT in my 15 with 70 HP at 43 MPH!!!
Teak Oil	posted 07-21-2005 10:17 AM ET (US) Before you get out the grinder and sander I would try raising the motor a hole or two. Also go for the jackplate and maybe even try a doel fin, its cheap and just might stabilize things. As you know a round bottom is not the best for top speed. Be sure to have a safety lanyard and life jacket ready for those high speed runs, you are going faster than Whaler ever intended on that hull
runpasthefence	posted 07-21-2005 10:56 AM ET (US) No racing, other than some VERY amateur stuff done on sunday evenings. As for why, well, I just like the speed. I also kind of like the idea of having the 15' that everyone talks about around the area. As for the money, it really isn't so bad. I get all of my parts at cost and do all of my own work (perks of working at a marine maintenance shop). Teak, the maximum vertical adjustment has already been done...short of a jack-plate. I'd like to stay away from a dole-fin, but I see where you're coming from. Probably going to add some good goggles to that safety list, the boat is already a tear-jerker.
Peter	posted 07-21-2005 11:24 AM ET (US) How about a helmet too! ;)
scaleplane	posted 07-21-2005 12:45 PM ET (US) Gotta say, 30 mph WOT with my 40HP Johnson is fast enough for me on my 15'. In fact, I usually choose to cruise around 20-22 very comfortably. Guess I'm getting old!
runpasthefence	posted 07-21-2005 07:46 PM ET (US) keep in mind, this is also a pleasure/ski boat. hence the forth coming jackplate. i dont want to permanently mount my motor that shallow. yeah i know im trying to accomplish a lot of this little boat, but what's a whaler nut supposed to do?
Binkie	posted 07-22-2005 07:30 AM ET (US) You just need more motor.Try a 2.4 Merc race motor. You`ll need a jack plate, but you will have to run the motor lower than the transom, due to the short racing lower unit, but the lower motor will give you more stability. The rounded bottom will make for a hairy ride, A pad would help, if you can get it right. Going fast is fun, your only limited by the "scared" factor.
runpasthefence	posted 07-22-2005 02:15 PM ET (US) I think the 2.4 is around 285hp? I know the 2.5 is 300, and close to 400lbs. Call me chicken, but 400% over the max-rated horespower seems a little overkill. We've got a couple of Yamaha 115s that I might try out after everything else is buttoned up.
jimh	posted 07-24-2005 09:15 AM ET (US) Administrative post
dnh	posted 07-24-2005 05:08 PM ET (US) runpasthefence, do you have any photos of your boat? I have a 1986 Sport and would like to see I photo of it with the 2005 90 on it...
runpasthefence	posted 07-25-2005 02:36 AM ET (US) No problem. I'll probably update this with more detail and update it with progress over the winter. http://photobucket.com/albums/v611/yeahtoast02/project%20Ambelina/
dnh	posted 07-25-2005 08:56 AM ET (US) runpastthefence, I just noticed you are in Charleston also. That's a nice picture of your boat with the keys in the background. I was out in mine yesterday in Beresford Creek, etc., perhaps I will see you out sometime. I'd actually like to get together some time if I get serious on the new engine and give yours a test run. Your boat looks pretty similar to mine but nicer. http://photobucket.com/albums/v672/dnh2
Barefoot	posted 07-25-2005 02:40 PM ET (US) Growing up I could get 47 out of my 15 with a 70HP on it. The boat's hull speed will not let it go much faster. Go buy a hydro and in the mean time be carefull not to blow the 15 whaler over.
BOB KEMMLER JR	posted 07-25-2005 03:50 PM ET (US) Mick-I'm planning on doing a lot of those same mods on a 15 Mischief with 115+hp merc tower.i think the mischief might have a slight edge over the reg sports because of the added weight of the cap and the added weight forward(plus they just look faster lol) due to the drivers position.Don't forget the steering wheel mounted trim unit and hot foot throttle.I'm also thinking of adding a 20 gallon or so belly tank under the foredeck area to get a little more weight up front.good luck and keep it right side up.
runpasthefence	posted 07-25-2005 05:40 PM ET (US) DNH, anytime you want to go for a run just email me at yeahtoast02@yahoo.com, I'll be back at The Citadel the 21st, but weekends are still usually free. Bob,I would love to see that boat. I wasn't aware the Mischief even existed previous to this winter. Definately a neat boat. It probably is better suited for what we're trying to achieve in speed, but I've never seen that proven. It would definately be interesting to compare. Im in the same situation with my fuel tank as well, but since the bow of my boat is much less protected and probably walked on more often...I'm trying to find a Pate or possibly a tempo to fit under my false floor. Im hoping to negate the added weight of that upcoming jack-plate. I am jealous of your 115 though. I mentioned earlier that I was going to bolt up a V4 Yam 115 for a weekend or so, but i think I've come to the conclusion that I'm just going to void my warranty to get another 20-30 horsepressure out of the three cylinder. Be sure to keep me updated, I'd love to see how things turn out.
myakka	posted 07-25-2005 09:05 PM ET (US) Bob I've been away for a while... YOU GOT A MISCHIF? Mike
where2	posted 07-25-2005 09:45 PM ET (US) If I could just find the racing lower unit off an OMC Sprint 75 (used on racing hydroplanes), and the right prop, I'm sure I could top that 47mph number Barefoot has...
dnh	posted 07-25-2005 09:55 PM ET (US) I do not believe the posts about there being a "top speed" of 48mph, etc. on the hull. I have no factual basis other than to say it doesn't seem to make sense. If you get the boat on an absolutely glass surface with a 115 on it, it sure as heck ought to go faster than the same boat with a 70. Maybe you got to put a weight in the front, etc. Maybe not. I have seen game warden 15s with 115xp Evinrudes on them. Ive seen two of these, old heavy 4cyl OMC engines. If it didnt make them run any faster than the 70, why would they be on there? It wasnt for towing or torque. If the boat is loaded carefully, the water is flat, and its trimmed correctly, it won't walk.
BOB KEMMLER JR	posted 07-25-2005 09:59 PM ET (US) Not yet Mike,but i may be taking a road trip to Mn to get one very soon.I have my eye on a few 115-150 Merc Towers too.My wife is planning on upping my life insurance policy as soon as the boats in the driveway hehe