posted 08-26-2011 09:28 AM ET (US)        

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Boaters really should try to get the boat and power they NEED for their waters and purposes, and avoid upgrading boat size or engine size beyond that point. Here is an example of how upgrading your purchase can leave you with little or no effective gain. I met a boater on my lake who had considered getting a boat similar to mine (Legend Xcalibur 16.5-foot with a 60HP BF Mercury 4 stroke). Instead, he had let the sales guy pressure him into spending an extra $6,200 on a 17.5-foot boat with a Mercury 115-HP FOURSTROKE. We talked about fuel costs, and he seemed happy with his purchase even though he was getting only about two-thirds the fuel range when compared to my boat. He bragged that his boat went 45-MPH according to his speedo, and when I expressed serious doubts over that claim, he challenged me to a race. So we went out, lined our boats up and hit the throttle.

We jumped out of the water at about the same speed and reached trimmed WOT at about the same speed. At this point he started to CRAWL ahead of me at about 1-MPH. Seriously, I can crawl way faster than the speed he was pulling away at. He was [angered] and confused. He spent many thousands of dollars on the bigger boat and larger motor. So for all that extra [money] and greatly reduced gas milage, all he could manage was a 1-MPH speed advantage--hehehehehe!

During this race, his speedo read 45-MPH and mine read 38-MPH, but our actual GPS speeds were 36-MPH and 35-MPH. [This variance] just goes to show you that you CAN'T trust speedo readings. If you don't have GPS speed, then don't even bother talking about fast your boat goes. Anyway, point is that he should have stuck to buying a boat that suited the size and type of waters he would boat on.

posted 08-26-2011 09:59 AM ET (US)            

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Yeah, it is hard to get an accurate reading on a speedo without manually calibrating it AFTER installation. Even a single degree difference on the sensor mount makes a big difference in the reading. GPS is the only way to go.

As for the race with the guy with the 115-HP, I suppose I should mention I had a Vengeance SST prop against what I am sure was the standard BlackMax aluminum prop. Also, he had more gear in his boat than I had in mine :) Hehe, he might have been slightly less [angered] if I had explained all that to him. But maybe this way he'll actually be encouraged to come read and join this forum to find out why he isn't any faster than a boat with only half the horsepower.

posted 08-26-2011 10:10 AM ET (US)            

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quote:

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If you don't have GPS speed, then don't even bother talking about fast your boat goes.

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Yes, I have been repeatedly making this very point here for about the last ten years.

posted 08-26-2011 11:01 AM ET (US)            

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I have a Lowrance paddle wheel speed sensor installed on my boat as part of a mini-NMEA2000 network. I installed this sensor in order to provide speed for the fuel calculations without having to purchase a much more expensive NMEA2000 gps sensor.

I find that the Lowrance paddle wheel reads a little slower than the GPS ground speed - on average about 1.5 mph slower, which isn't nearly as bad as a lot of the reports we see.

posted 08-26-2011 06:36 PM ET (US)            

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Naw, he originally wanted a similar 16.5' Xcalibur with a 60HP or 75HP (75HP is max allowed on that kind of boat).

But his wife told him he only gets to buy ONE boat and he had better get what he wants the first time. Then the sales guy pressured him into believing that he needed the bigger motor in order to be 100% sure he has enough power....and so he then needed the one-foot-bigger boat to fit the bigger motor. The fact that the performance between our two boats is roughly the same; kind of put a damper on his boat pride.

In hindsight, it was cruel of me not to explain that his extra gear and lack of SST prop made a difference in our race. I'll be sure to mention it to him the next time I see him.

posted 08-28-2011 10:07 AM ET (US)            

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Regarding accuracy of boat speed measurement, I used to have a Lowrance SONAR with a paddlewheel speed sensor input. There were some calibration controls for the paddlewheel speed sensor. Using these controls I was able to calibrate the paddlewheel speed to match the GPS speed over a very wide range, from slow idle to full-throttle, so that the variance between the two was always less than 1-MPH, and at lower speeds the variance was nil.

Most GPS receivers do not measure speed at all, and deduce speed by calculating the time elapsed between successive position fixes. The accuracy of this method was the topic for an interesting discussion in SMALL BOAT ELECTRICAL. See

Accuracy of GPS Receiver Speed Measurements
http://continuouswave.com/ubb/Forum6/HTML/002179.html

As for a general inference or conclusion to be drawn about the value of boats based on the narrative of the experience of two owners of non-Boston Whaler boats who competed on boat speed, I do not see very much validity or insight. The "return" from a boat is much more complicated than the ratio of its cost to its top speed, which seems to be the parameter employed in this comparison.

posted 08-28-2011 01:21 PM ET (US)            

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For that increased cost, your friend got a bigger, more capable boat. It may not matter, if he never takes the boat anywhere else, but if he decides to take it on a vacation to another location, his boat may be more suitable than yours.

I don't understand the point of this post, since you're comparing apples to oranges. In 1985, an 18' Outrage cost much more than a 17' Montauk, but they are very different boats with much different capabilities.

Additionally, every hull has a theoretical "hull speed" - where more HP to a certain speed will help dramatically, but beyond that point, more HP produces diminished returns. For instance, on an 18' Outrage, a 115 HP motor can often produce speeds in the mid 40's, whereas a 150 HP motor may only push the boat four or five MPH faster - to just less than 50 MPH. That is because the 18' Outrage hull needs a LOT more HP to push it much beyond 50 MPH - 45-47 MPH is about where it maxes out without pushing into the realm of 'less safe'.

Likewise, most boats have what I call a "happy" speed. Where they will cruise well...you can feel the hull lift out of the water and just settle in and 'feel right'. If you underpower the boat enough so that the engine must work very hard to reach the "happy speed", you have generally diminished your savings - unless you operate in conditions that don't ever really allow you to run at that speed. An example of this is the 18' Outrage, again. Put a single 90 HP motor on it, and it will reach "happy" - about 26-28 mph. But the 90 is straining and operating in an inefficient zone. Add just a few more HP (and perhaps another cylinder and some more displacement), and you get a much more economical and comfortable rig.

posted 08-28-2011 01:28 PM ET (US)            

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Also, neither of your boats have max hp. Yours is rated to 75 hp, and his is rated to 150 HP. In fact, you are much closer to the max HP rating on your boat than he is.

Here are the specifications on his boat:
Centerline Length 17'6"
Beam 90"
Hull Depth 41"
Inside Depth 26"
Aluminum Thickness .100
Maximum Horsepower 150
Maximum Capacity 1625 lbs.
Hull Weight 1225 lbs.
Bottom Width 76"
Package Length 19'9"
Package Width 92"

Here are the specifications on your boat:

Centerline Length 16'6"
Beam 82"
Hull Depth 37"
Inside Depth 25"
Aluminum Thickness .100
Maximum Horsepower 75
Maximum Capacity 1475 lbs.
Hull Weight 1045 lbs.
Bottom Width 69"
Package Length 18'4"
Package Width 82"

His boat is larger in every dimension. In short, he has the more capable boat.

The really bad news is that both of your boats can sink, no matter how fast they'll go.

posted 08-28-2011 03:04 PM ET (US)            

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Motor mounting height and propellers can make a huge difference. I gain 8mph by changing props and adding a jackplate. I was down atleast 4mph because of the motor being mounted the lowest position.

Next time the original poster is out at your boat, look at the mounting bolts on your engine. Top bolts are the lowest mounting position. Compare them to your neighbors boat, you might find his motor is mounted too low. If its different, you can choose to share that information with him or not :)

posted 08-28-2011 03:10 PM ET (US)            

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Motor mounting height and propellers can make a huge difference. I gain 8mph by changing props and adding a jackplate. I was down atleast 4mph because of the motor being mounted the lowest position.

Next time the original poster is out at your boat, look at the mounting bolts on your engine. Top bolts are the lowest mounting position. Compare them to your neighbors boat, you might find his motor is mounted too low. If its different, you can choose to share that information with him or not :)

posted 08-29-2011 02:04 AM ET (US)         

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Regarding the subject of this discussion, and Garrett's mention that both boats had Mercury engines, it should be noted that Mercs require a specially calibrated speedometer.

It seems that the gearcase speedo pickup is very efficient, and must be used with a Mercury branded speedometer. If not, the speed reading will be about 15% too high when used with an aftermarket speedometer such as the Teleflex and Faria brands.

posted 08-29-2011 09:24 AM ET (US)            

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If you had really big tank, lets say 50 feet across, that was 30 feet tall full of water and a 3/4 inch hose that was 30 feet long hanging straight up and down full of water. Which one would have the higher pressure at the bottom?

This relates to the pitot tube speed indicator.

Rick

posted 08-29-2011 10:59 PM ET (US)            

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Larry makes an important observation: a pitot tube speedometer is not a universally calibrated device. The gauge which shows speed must be calibrated for the pitot tube that is providing the pressure differential. I doubt that there is a universal standard for this among all pitot speedometer gauges.

It is also clear that some pitot tube speedometers are more accurate than others. This seems entirely reasonable. We're talking about a analog measuring systems. Accuracy can easily be affected by craftsmanship and precision.

posted 08-30-2011 11:03 AM ET (US)            

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Didn't see it mentioned as I skimmed the discussion.

Pitot tubes provide an idea of speed through the water. They are not impacted by current or wind.

GPS provides speed over the bottom. They are impacted by current and wind.

JimP

posted 08-30-2011 03:13 PM ET (US)            

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Here in Chesapeake Bay with minimal current, my YAMAHA digital speedometer using the pickup that is built into the lower unit read 1-2 different than the GPS.

Sometimes it's dead on like yesterday the GPS was reading 41.8 and the YAMAHA gauge said 42. Rounding up it was dead on.
Water pressure speedos aren't as bad as some make them out to be.

posted 09-25-2011 09:10 PM ET (US)            

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I checked the YAMAHA Command Link pitot speedometer yesterday comparing it to my handheld GPS (no electronics on board at the moment). It reads down to 3 mph and is never more than 1 mph different from the GPS from 3 to 50 mph.

The YAMAHA pitot speedometer uses a pressure transducer to convert the pressure to an electrical signal and put onto the YAMAHA version of NMEA 2000, Command Link (Plus). I assume this is how they achieve good accuracy.

I very impressed with the accuracy of this system compared to the old Teleflex pitot speedometers. My GPS recorded 83.9 miles and the YAMAHA Command Link recorded 83.7 miles traveled which is derived from the pitot speedometer.