How are factory top speeds figured?

[superbenk]

Calm night tonight on the lake and I had 3 kids , my wife & I in the boat (2008 Four Winns H200 w/ carbed 5.0L). The brochure for the boat says it should too out at ~53ish but I only hit ~43-45 according to my iPhone GPS. WOT was at around 4500 RPM & I had adjusted trim as best as possible. Kids were up in the bow with my wife & I in the cockpit & roughly 1/2 tank of gas. Why am I coming in at nearly 10mph under the brochure? Boat is immaculate & only had 17.5 hrs when we bought last fall. It runs like a top as far as I can tell but I'm wondering if something is wrong.

 

[NYBo]

Your a little low on WOT revs and you have a lot more weight than the factory had in it to get that number.

 

[MARV1]

Calm water won't get you speed, a lil ripples is ideal.

 

[Scott Danforth]

boats are generally tested with 1/4 tank of fuel, two people, and a 6" chop.

your WOT RPM is about 400-500 RPM low. you may want to make sure the throttle is opening up all the way.

 

[jimbo_jwc]

Put kids on back seats with wifey next to you and trim , Mine goes faster that way with smaller dia. 2" more pitch SS 3blade prop and more WOT rpm .Chop on water must give little air for less resistance under hull .My old Woodson cathedral hull was faster into wind .

 

[Bondo]

Calm night tonight on the lake and I had 3 kids , my wife & I in the boat (2008 Four Winns H200 w/ carbed 5.0L). The brochure for the boat says it should too out at ~53ish but I only hit ~43-45 according to my iPhone GPS. WOT was at around 4500 RPM & I had adjusted trim as best as possible. Kids were up in the bow with my wife & I in the cockpit & roughly 1/2 tank of gas. Why am I coming in at nearly 10mph under the brochure? Boat is immaculate & only had 17.5 hrs when we bought last fall. It runs like a top as far as I can tell but I'm wondering if something is wrong. [h=2]How are factory top speeds figured?[/h]

Ayuh,...... Optimistically,.....

Without a Race-prepped boat bottom, perfect conditions, 1 gallon of gas, 'n a 100lb. operator, I really doubt you'll see 53mph,....

 

[Fastatv]

I agree with about all these fellows....especially about the 6" chop and moving the family back towards the stern. You might get a little more out of her. I'm thinking 47 to 48 ( max ) with the family. If you really want to see what she will do, take it out by yourself, in a 6" chop. It might hit hit 50 or so.

 

[Scott Danforth]

you can check with boattest.com and see what they got for top speed, etc.

 

[QC]

And you won't see that speed either ^^^^^^ There is not one boat, that I have ever been on, that meets spec sheet, or even boattest.com speed. Not only do you have the kids, you have ice chest, anchor, stuff, more sruff, beer, more beer AND they had the boat setup perfectly as Bondo notes. I would look for 48 under ideal conditions, and be happy if I got there. My boat, same prop, empty with me alone, I can get 57 out of her, and she tested at 62. 5 MPH below test seems pretty standard in my experience.

 

[superbenk]

Well you're all certainly making me feel better. I know I've hit 50ish before so I won't worry about it.

 

[jimbo_jwc]

Ayuh,...... Optimistically,.....

Without a Race-prepped boat bottom, perfect conditions, 1 gallon of gas, 'n a 100lb. operator, I really doubt you'll see 53mph,....

Is there a occupation Speed Test Boat Jockey for manufactures ? Lighter wife n less food for kids .

 

[Bubbasboat]

xxxxx

 

[NYBo]

They also test going slightly downhill!:lol:

 

[KC8QVO]

Calm night tonight on the lake and I had 3 kids , my wife & I in the boat (2008 Four Winns H200 w/ carbed 5.0L). The brochure for the boat says it should too out at ~53ish but I only hit ~43-45 according to my iPhone GPS. WOT was at around 4500 RPM & I had adjusted trim as best as possible. Kids were up in the bow with my wife & I in the cockpit & roughly 1/2 tank of gas. Why am I coming in at nearly 10mph under the brochure? Boat is immaculate & only had 17.5 hrs when we bought last fall. It runs like a top as far as I can tell but I'm wondering if something is wrong.

If you typically run the boat loaded then tune it to that type of load. I did the same thing, although on a much smaller boat. With one person and no gear the boat would go like a bat out of you know where, but as soon as my brother and I loaded up for a day on the lake it bogged down. I took the prop down 2 pitch sizes and gained 3-4mph in average conditions. The biggest number I saw was 9mph above where I was prior, but with chop and down wind so I would consider it an outlier.

I would be curious to know how much of a difference a prop change would do in your scenario. You should be able to get the specs for the RPM range for that boat and set up. With a load it might be wise to shoot for the low end of the RPM range, or without a load to shoot for the high end. Others may be able to comment on this one, but the general idea is to get the WOT RPM's in the specified range. When you have a load that changes so, too, does the work the motor has to do = RPM's change. If you never really run at WOT and are not concerned with acceleration/hole shot or step times you may never know if your set up is ideal or not. As others have indicated - your RPM's seem low = your gearing isn't ideal. I doubt changing the position of the people in the boat will make much difference, but it would be neat to document all the changes and see what the affect is on the speed/rpm with each change, if you have the opportunity and time.

 

[superbenk]

Ran it out in chop today with the same people in the boat and approached 4800 RPM before it started to cavitation & around 48 MPH give or take. I wonder how much drag the Bimini top (wrapped up) causes? I've considered rep roping, but it has the factory spec'ed prop now & I kind of want the best of both worlds, faster out of the hole *and* top end. No way I'm getting both without more motor, so I'm probably best as I sit now.

 

[KC8QVO]

Too much prop will slow you down and slow down your acceleration. Just in my example I went from a 13 pitch to an 11 pitch (down 2 sizes). That gave me more torque at the prop and, as I said, I boosted the top end speed 3-4mph - with a load. I never compared the unloaded speeds because it was never a concern. When I'm on the lake I have lots of extra fuel, spare motor, and gear so it all adds up.

 

[superbenk]

I've been considering a 4-blade 19" to replace the factory 3-blade 21". It's usually at least the wife & two kids with me, so the torque would be nice. That said, it's really not broken so maybe I shouldn't fix anything

 

[QC]

Ran it out in chop today with the same people in the boat and approached 4800 RPM before it started to cavitation & around 48 MPH give or take. I wonder how much drag the Bimini top (wrapped up) causes?

First, what you experienced is Ventilation. If there was no porpoise, and you were not 100% trimmed out, then I would try and move some weight aft. That will gain you some more trim, and hopefully some more speed. You want full trim and just at (below) the speed she will porpoise. If she blows out (ventilation) before porpoise or full trim, then there is some speed to be found with weight distribution. If we can get her faster, and porpoise is the limit, then we talk trim tabs. Isn't this fun?

Below 50 I wouldn't worry about the Bimini, up, down, or deployed.

 

[jimbo_jwc]

Is this true?

Flying boats had to have step in hull to to break water stick ,must have give air to release loosen maybe surface tension ?

 

[jimbo_jwc]

They also test going slightly downhill!:lol:

Which way is that on a river ? HaHa
River current speed adds /subtracts MPH on gps not speedometer ?
Interesting when people experiment with boat/prop/engine set up to make more fitting to their applications cause all the variables and like Harleys no two alike ,just similar with same forces to overcome ,boiling down to HP.