Your On-Line Port'o'Call

Previous Thread
Next Thread
Print Thread
Rate This Thread
Page 1 of 5 1 2 3 4 5
#323358 - 06/25/07 10:01 PM Let's talk TRUE Top Speed.(GPS Verified of course)  
Joined: Apr 2007
Posts: 41
jscott116 Offline
Lieutenant JG
jscott116  Offline
Lieutenant JG

Joined: Apr 2007
Posts: 41
I have read the given top speeds of some of the many different boats on here. It is interesting to see what the top speeds are given for the different style/weight of the boats. I don't know if everyone uses a GPS or if they go by their speedo... If they in fact use a GPS, Something seems weird about my boat. Some of the boats on here are larger, heavier, with less horsepower and still post higher top end speeds. I have a 21 foot bowrider that has a dry weight of 3200#. It has the 350 Mag with an Alpha One drive(1.47 ratio). I am running the OEM Alpha 4 aluminum prop that is an 18 pitch. WOT RPM is 5200. With 25 gallons of fuel and four adults top speed is 48.2 mph. When I bought the boat, I figured that it would run probably 53-54mph. Not the case. I understand that I am only running an 18 pitch prop and that a larger pitch would yield a higher top end, but my WOT rpm's are exactly where they need to be. What is the deal?

After saying all that, I did not buy the boat for top end speed. I got the 350 Mag for the torque and holeshot needed for watersports. I plan on getting a high five this week(19 pitch) to help out even more. Watersports is my main goal, but I have to say that I was still a little disappointed with the top speed even though I run WOT 0.05% of the time. I just like to see the look on a GF boaters face when a bowrider comes around them!


East Central Oklahoma
A Word from Our Sponsors
#323359 - 06/25/07 10:10 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Jun 2004
Posts: 8,946
Silverbullet Offline
Admiral
Silverbullet  Offline
Admiral

Joined: Jun 2004
Posts: 8,946
Boise, ID
Top speed is important to me and something I have been taking into account during my search. Two of the boats I have been looking at both max out with VP 5.7GXI. The top speed of both of those boats is in the low 50's. That was a little disappointing for me as it is something I look for, though I don't spend a ton of time at WOT.

A boat I test drove recently was solidly into the mid 60's and it was a great ride. There are many variations that impact the top speed of a boat, just like a car. Even the same boats with the same power plant will vary in speed. A boat is running through water which has much more drag than a car in the air, but follows many of the same principle. Variations in the design of the hull impact many things including top speed. The conditions in which you boat also make a big difference in the power the engine can put out.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


#323362 - 06/25/07 10:25 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: Silverbullet]  
Joined: Jun 2006
Posts: 96
Pacfanweb Offline
Commander
Pacfanweb  Offline
Commander

Joined: Jun 2006
Posts: 96
Wake Forest, NC
Your engine might have enough oomph to spin another prop at that same rpm. If so, there's your 50+mph.


2007 Bryant 219
2004 Z71 Suburban
#323365 - 06/25/07 10:33 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Dec 2002
Posts: 28,862
seabuddy Offline
Admiral
seabuddy  Offline
Admiral

Joined: Dec 2002
Posts: 28,862
GPS, two way average, is true top speed. But it still varies day in/day out. Lots of reasons.

Boating is the passion of most of the members, however. Passionate folks often fudge. Hey, at a bar, I may fudge. On the board, I don't.

Note, some members will mention something when the speeds are out of line, including me.

Question, have you tried various trim postions and moving weight around within your boat?

#323366 - 06/25/07 10:37 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Dec 2003
Posts: 3,874
athiker Offline
Admiral
athiker  Offline
Admiral

Joined: Dec 2003
Posts: 3,874
Lake Norman, NC
Your aluminum Alpha 4 is only recommended for engines putting out less than 250hp by Mercury Marine.

Merc Propellers: Alpha 4

 Quote:
For V-6 outboards and Alpha sterndrives up to 250 hp


You may be getting some blade deformation at your current top rpm/speed. I also think you are running too low a pitch. I run an alum Black Max 3 blade 21p and think my holeshot is great. I have a 2000 5.7L 260hp pushing a 21 footer. I'm 10hp over the recommended hp for the Black Max but its what came w/ the boat. I have run a 20p 4 blade with nice results and tried the same prop in an 18p w/ very poor results...way too revvy.

I would think you would have a monster holeshot w/ the High Five and that engine and size boat. I bet if you went to something like a 20p SS 4 blade you might get just as good a hole shot as now, at least all you would need, plus a much better top end. I'm just speculating based on the lousy performance I had w/ the 18p prop I tried. It was revving so much even while trying to pull a wakeboarder at a relatively low speed I had to go back to the dock and swap the prop...it just wouldn't go!

EDIT: I guess I didn't really answer your question. My top speed has been measured right at 50 mph by GPS. This has surprised some on this board as too low for my boat/engine but it seems to run like a top. I also regularly pull some pretty big guys up on slalom with ease so have never felt lacking in hole shot. You have, I believe, 40 more hp than me so I would think at normal elevations, you would be into the 50s w/ a different prop. What is your boat btw?...make & model?...year?


Last edited by athiker; 06/26/07 07:36 AM.

2000 Cobalt 206 5.7L EFI Alpha 1
#323368 - 06/25/07 11:04 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: athiker]  
Joined: Apr 2007
Posts: 41
jscott116 Offline
Lieutenant JG
jscott116  Offline
Lieutenant JG

Joined: Apr 2007
Posts: 41

Here it is! Can you believe that this beauty will not run 50!!!



No just kidding. Here it really is. 2007 Chaparral 210 SSI. This thing is my pride and joy.



East Central Oklahoma
#323370 - 06/25/07 11:09 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Apr 2007
Posts: 41
jscott116 Offline
Lieutenant JG
jscott116  Offline
Lieutenant JG

Joined: Apr 2007
Posts: 41
Seabuddy, I have tried different trim positions, the only problem is that you can barely get to 1/4 trim without this boat porpoising. the boat is kind of short to have all that weight on the back I guess. I wish the gas tank was a little farther forward.


East Central Oklahoma
#323371 - 06/25/07 11:19 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
Do you happen to know your prop's diameter?


-YOLO
#323373 - 06/25/07 11:22 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: D-Rod]  
Joined: Apr 2007
Posts: 41
jscott116 Offline
Lieutenant JG
jscott116  Offline
Lieutenant JG

Joined: Apr 2007
Posts: 41
I think it is 14", but I am not positive.


East Central Oklahoma
#323376 - 06/25/07 11:32 PM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
Well, I will spit my thinking out:

18p seems too small for a V8 in your boat. I'm going to guess the high-five will help some, but too much blade area for top speed. With that much power in your boat, I would look for a 4 blade that is large in diameter and has a large amount of blade area. This will help the prop bite (takeoff will be good) and should help on the top end as well. You probably want your rpms around 4800-4900 if you have 4 people and gear onboard. Your engine has some torque. Use it for your holeshot.

How does your boat handle sharp turning? What about trimming out? Have you trimmed up to the point the prop looses bite and then lowered it just enough for it to "bite"?

With a 350 Mag, I would run stainless.

A 350 Mag in a your boat should be plenty of power, so holeshot should not be a concern. I would look for a good overall preforming prop. If your boat is properly propped, you should not have hole-shot problems.

Derek


-YOLO
#323379 - 06/25/07 11:39 PM Re: Let's talk TRUE Top Speed.(GPS Verified of cou [Re: D-Rod]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
Your prop is probably has a 14.5" diameter.

You might consider a Rev 4 prop. Look for a 14.625 x 19.

Merc part number: 48-857026A46

Seabuddy is the prop man...he might have another approach.

Something else to consider trying is the 3-blade prop route, like the Enertia. It is a 3 blade 14x19 prop. Again, how effective a 3-blade is depends on how much life your hull design needs. Sorry I do not have real-world experience with your boat.

D



-YOLO
#323382 - 06/25/07 11:46 PM Re: Let's talk TRUE Top Speed.(GPS Verified of cou [Re: D-Rod]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
BTW: I have seen 40.5mph WOT on the GPS. Not too impressive until you consider it's a V4 pushing 22ft of boat.

Then again..it is a pretty flat bottom.


-YOLO
#323389 - 06/26/07 01:56 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: D-Rod]  
Joined: Jan 2003
Posts: 15,089
Al Offline
Nautical Alchemist
Al  Offline
Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
On the right day, I have seen 34mph on my tub - GPS verified, of course. Its maintainable too, since at that rate, the fuel consumption lightens the boat very quickly.

Last edited by Al; 06/26/07 01:56 AM.

President and CEO - Napmoor and Doolittle.


2004 Mercury 270 Dinghy.
2016 Grand Design Reflection 29RS 5th Wheel
2016 GMC Sierra 2500HD SLT 6.6L Diesel

previous boats:
1995 Carver 325
1999 Four Winns 268
1999 Four Winns 225
1996 Rinker 180
#323392 - 06/26/07 03:36 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: Al]  
Joined: Dec 2002
Posts: 28,862
seabuddy Offline
Admiral
seabuddy  Offline
Admiral

Joined: Dec 2002
Posts: 28,862
There are props that can tend to hlep with that porpoising.

#323408 - 06/26/07 06:36 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: jscott116]  
Joined: Oct 2004
Posts: 7,510
BillyB Offline
Admiral
BillyB  Offline
Admiral

Joined: Oct 2004
Posts: 7,510
Peoria, Illinois
As you are being advised, you need a diiferent prop. I am not sure who told you that 5200rpm was ok for a 350MAG MPI, but it's WOT rpm range is 4600 to 5000. So if you put a 21 pitch 3 blade on there, your WOT rpms will probably drop to about 4700 and you'll hit that 53 mph you had hoped for.

(I hope to be able to use my dad's handheld GPS this weekend to get my true top speed. I'll take a reading with the current, and one against, and see how it works out.)

Last edited by BillyB; 06/26/07 06:44 AM.

I'm just happy to be here!



#323411 - 06/26/07 06:59 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: BillyB]  
Joined: Oct 2003
Posts: 7,506
captkevin Online content
Admiral
captkevin  Online Content
Admiral

Joined: Oct 2003
Posts: 7,506
Chicago, IL
Trim tabs or smart tabs would help you out with the porpoising issues and allow you to utilize your trim to increase speed. 5200 is definately beyond recommend wot - my 5.7 mpi range is 4600 - 5000 wot. Stainless 4 blade would help out.

My 23'6" boat wt 4100# will get up to 4900 wot & aprox 51-52 gps mph.

Last edited by captkevin; 06/26/07 07:01 AM.

2004 Rinker 232
2010 Dodge Ram Crew Cab Laramie 4x4
#323412 - 06/26/07 07:06 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: BillyB]  
Joined: Jan 2004
Posts: 12,012
WaterMutt Offline
Bilge Rat
WaterMutt  Offline
Bilge Rat
Admiral

Joined: Jan 2004
Posts: 12,012
Massachusetts
A prop is only good up to a certain rpm, then it begins to become inefficient and will begin to cavitate as it will not allow enough water through to bite. I can get up to the mid fifties with my boat, and that is with a 4 blade prop. But that is exceeding the stock engine rpm limits. I think I could get a bit more, but the prop is limiting me, IMO, and is extremely inefficient. I've never run the numbers to see though. I don't care much about top speed, my main purpose is sports and cruising and the 4-blade does well for me.
If you are interested in speed, stick with a 3 blade, go SS, jump up to something in the 21px14.25-14.5 range. This will effect your holeshot somewhat, but increase your top speed.
If you want to keep some holeshot, bump to a SS 19p around the 14.5 inch diameter.


Malibu Wakesetter 23XTI
Bryant 214 Limited (gone, but not forgotten)

"That's my boat..."
-Forest Gump

#323419 - 06/26/07 07:59 AM Re: Let's talk TRUE Top Speed.(GPS Verified of cou [Re: WaterMutt]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
I typed all of his information into Merc's prop selector. The highest pitch it recommended was 19".

Stainless alone should help you gain 1-2mph.

D

Last edited by D-Rod; 06/26/07 09:17 AM. Reason: Removed a line

-YOLO
#323432 - 06/26/07 09:09 AM Re: Let's talk TRUE Top Speed.(GPS Verified of course) [Re: D-Rod]  
Joined: Dec 2003
Posts: 3,874
athiker Offline
Admiral
athiker  Offline
Admiral

Joined: Dec 2003
Posts: 3,874
Lake Norman, NC
I threw your #s in a prop calculator and, assuming your tach is accurate, you currently have over 20% slip.

Prop Calculator

Actually, I'm in that area too, so I'm not sure what that says except maybe I could benefit from a SS blade too! I thought it was more typical to be around 15%, maybe others can chime in about that.

I got the same results as D-Rod throwing your #s in the Merc Prop selector tool...mostly 19p. If I throw my #s in...21p/4600/50mph and year 2000 I get Alpha4 20p, Enertia 22p and Rev4 21p! There is no input for boat length or weight btw.

So we are both slipping about 20%, have the same block but you have more hp and you are getting a 19p rec and I a 21p. I can only figure this is explained by our recommended rpm ranges. I believe my 2000 is spec'd at 4400 - 4800 while yours is actually spec'd at 4800 - 5200 per the Merc website. So Merc seems to be saying you can benefit from the lower pitch for holeshot, and still get a good top speed by revving up a good deal higher than was recommended for my 2000 EFI engine. Comments?...am I off base? I think this new 5200 rpm top must have recently been raised from 5000 that I and others recall from memory?

350 MAG MPI - 300hp


EDIT: I also want to note that from looking at pics that the Merc Alpa4 looks to have a more full ear blade design than the Piranha 4 blade that I used in the 18p/20p comments above.

Last edited by athiker; 06/26/07 09:31 AM.

2000 Cobalt 206 5.7L EFI Alpha 1
#323434 - 06/26/07 09:14 AM Re: Let's talk TRUE Top Speed.(GPS Verified of cou [Re: athiker]  
Joined: Jun 2005
Posts: 9,255
D-Rod Offline
Rock Chalk Jayhawk
D-Rod  Offline
Rock Chalk Jayhawk
Admiral

Joined: Jun 2005
Posts: 9,255
Back Stateside
That's nice to see Merc upped the RPM specs.

I'm going to go edit my previous post.


-YOLO
Page 1 of 5 1 2 3 4 5

Moderated by  Admin 

Sponsors
New Topics
Must be that time again.....
by GoFirstClass. 12/04/18 06:18 PM
So Glad Harvard Graduates can afford Expensive Watches
by Justification. 12/04/18 05:27 PM
Trailer Weight Distribution
by MarkHB. 12/01/18 10:56 AM
Holiday DEALS
by KCook. 11/23/18 03:51 PM
Persistence Pays Off
by GoFirstClass. 11/17/18 07:50 PM
Quick question
by Bones. 11/15/18 01:10 AM
Wow! Great to see familiar login names!!!!
by Bones. 11/14/18 11:51 PM
Shopping for another boat...
by Dave R. 11/06/18 05:46 PM
'This site is not secure'-- I'm afraid is true...
by Frantically Relaxing. 10/28/18 10:26 PM
Boating On The Columbia
by GoFirstClass. 10/24/18 11:19 PM
Who's Online Now
1 registered members (Dave R), 76 guests, and 4 spiders.
Key: Admin, Global Mod, Mod
Newest Members
okielaker, Rbt18, oldnamwaterskier, farmermike, FrankC
5463 Registered Users
Forum Statistics
Forums23
Topics37,219
Posts563,286
Members5,464
Most Online252
Aug 5th, 2017
Powered by UBB.threads™ PHP Forum Software 7.6.0