optimum speed for fuel economy m26

[seahouse]

Thanks for that list Matt - I just bookmarked that post for future reference. No local suppliers of those parts around here, I'd be ordering everything, so needing the 3rd T, or getting the wrong length cable would be inconvenient to discover later on. Note it's “NMEA” 2000 fittings; asking for “NEMA” might get you fittings for your house.

-B.

[BOAT]

Man oh Man that's the ticket for sure skipper! Captain mastreb to the resue. That is the deal for me and it takes all the guesswork out of the whole power boat issue and answers all those questions wit hone easy fix.
Thanks greatly mstreb (See, I told you guys he would know)
I'm gonna order that stuff you mentiond Captain right away - the only thing I need to decide on now is a Chartplotter - any recomendations out there? Is the 4 inch 4 seris garmin enough or do I go for a 5 inch 5 series? (By the way, they have a 7 series out now! Yup SEVEN INCH screen and that might do good for thoth of us with bad eyes). But I don't want to hang a monstrosity if I don't need it.

What's better, RayMarine? Lorance? Garmin?

[seahouse]

Hey BOAT! I just was thinking the same thing, so I started a new thread on display size.

[Catigale]

Matt...can I integrate that NeMA into my Oracle ERP ....any Sage advice on that?

(Ducks)

[drams_1999]

Kurz thanks for the earlier post....that kind of information can be extremely helpful.

[mastreb]

Matt...can I integrate that NeMA into my Oracle ERP ....any Sage advice on that?

(Ducks)

Hi Stephen,

Yes, here's what you need:

Maretron NMEA 2000 VDR-100 data logger http://www.maretron.com/products/vdr100 ... sh%20drive
NMEA 2000 network T
2' NMEA 2000 drop cable

You'll need the included Maretron data conversion software as the VDR logs in EXT3 Linux file system. Import the data and export to CSV format, then use Excel or Access via an ODBC Oracle driver to insert the data into your ERP for analysis.

You could automate the process using Java running on a Linux platform and the JDBC drivers for Linux, but it would take a tiny bit of programming.

[BOAT]

Hey Captain Matt! You sayin that the data from the NEMA 2000 is available as ASCII or text or somthing? So I could stream that info into Excel?

If I can capture that in Excel what's to stop me from using Excel to navigate an autopilot on 'boat'?? Could I not just control a little servo on the wheel using excel? Sure seems a lot eisier and cheaper than adding a stupid 1000 dollar monstrosity to the wheelhous. So what do we need? Just a guy with DC servo expertise?? Some motion control guy to set us up with the servo? I'm sure we could work out all the calculations in Excel to properly steer the boat - that part should be easy.

[bastonjock]

There are just too many variations where i sail to get an accurate fuel consumption using the rpm of your engine,ive found that by adjusting the angle of the engine effects the speed of the boat,and then there is tide and wind to consider and wave height also,i can potter around all day getting great fuel economy,if i time the tides correctly and have the wind at my back i can go for miles.

If i want great fuel economy i have to go with the tide,i can come out of my home port and experience 2 hours of near slack water then 4 hours of tides up to 3 knots and another couple of hours of slack.

If you have to head into the wind and waves then the BF50 just guzzles the fuel,also motor sailing helps keep the gas bill down and at £1.40 a liter i do tend to watch the consumption

[seahouse]

Matt...can I integrate that NeMA into my Oracle ERP ....any Sage advice on that?

Hah hah, the spelling, Cat!

Yes. And if you want the fittings for a fish-finder, google search under “Finding NEMO”!

-B.

[K9Kampers]

"Yes some new world class race boats now have rotating mast and now have adjustable dagger boards and "

This brings up a good point for another post I have been thinking about. Now that I see how easy it is to remove the daggerboard I am already thinging about building a NEW daggerboard with a trim tab on it. for racing that I can control from the cokpit

Thass funny! (some of the best one's come after April 1st!)

[BOAT]

Really! I know it sounds silly but think about it! Way down at the end of the daggerboard just have about bottom aft 12 inches of the daggerboard able to articulate about 2 or 3 inches of trim. You know, ilke cut a little 3 inch sliver from the rear of the DB to about 12 inches up from the bottom of the DB? You know? Like an airplane flap or trim tab?? (Am I making any sense?)

Here is what I was thinking - your in heavy wind, the boat is healing bad, you would start to reef because it's rounding up, so instead you pull a littler rope that moves that little flap on the end of the daggerboard just a little bit to the heeling side and 'Presto!" the boat digs in a little better and stops rounding up and you go fater (??? would it go faster??)

I dunno, I need the engeneer guys to figure that out - I'm just sayin that a trim tab on the DB would be pretty easy cuz the DB is so easy to remove an modify.

Okay, so I'm dumb, I'm sorry - I was just thinkin.

[BOAT]

Thanks for the tips - I want to do some night runs to Avalon too so I figured on a lot of WOT on those legs during the times of night that the wind might die.

I don't know about where you are, but up here that's asking for trouble. Nothing like a 4 ton water logged semi buoyant log through your hull to ruin your evening.

Sorry I missed this Captain Bob, but yeah, we see the darndest things out there - I think the worst things we see are cargo containers - it's always amazing to me how many cargo containers we find floating inches from the surface. The deadheads are not too common like they are up in the more forested areas whe you guys are and the guys in Washinton and Oregon but we do get some.

Ususally the night stuff is during a full moon with other people meeting us. It's sort of rare that we cross at night without meeting others and even more rare to do it under a full throttle (in fact, since all I know are traditional sailboats I have NEVER tried to do ANYTHING under a full throttle). That's all new to me. The fisherman here do it but enven they tell me trawling speed is usually sufficent for them.

I'm not sure what to do about floaties - never been a stinkboat operator - any advice? Any of you guys do it? I'm just rying to figure out how to put down a lot of miles in a hurry to get ahead of schedule.

[mastreb]

I know something about fluids, and something about engines, but never gave any thought to power boats and how it all works together, especially with three distinct operating regions. I'd love to see some actual (informal) test results with one of the Mac power sailers.

So you are correct in the simple case of a single efficiency curve, but there's more than one:

1) Parasitic engine loss: At Idle, an engine is 0 percent efficient because it's producing no useful work, but still consumes fuel. At 100% WOT, the engine is producing the maximum amount of power it can create, and for the majority of engines, this speed is the most efficient in terms of power generation (but not in terms of speed generated from power, which is limited by...
2) Displacement drag: Pushing water out of the way of the hull is a second curve that dominates the efficiency equation below the boat's hull speed, and it curves the opposite direction: At 0 knots, the boat has the least displacement drag, and at hull speed it has the most. The intersection of the parasitic engine loss curve and the displacement drag curve is actually the most efficient operating speed for a boat at low speed, and that speed is about 4 knots on my boat, as determined by my chart-plotter's maximum range calculation from my engine cable's consumption data. Displacement drag is easy to see increase by looking at your wake and bow-wave. When you see noticeable turbulence, you're generating enough drag to limit efficiency.
3) Laminar flow drag: Water moving across the wetted surface of the boat also creates drag based on the surface fairness of the hull and the amount of water in contact with the hull. This drag remains very low at low speed, and reaches its maximum at the boat's maximum planing speed, which on my boat is about 18 knots.
4) Aerodynamic drag: The portion of the boat out of the water (it's windage) is subject to an increasing drag curve as it pushes against the atmosphere. This curve is at about the same upward slope as Laminar Flow drag, and because they both impact the boat the same way and rise at the same time, they're often lumped in together. It too reaches its maximum at the boats maximum planing speed.

There are other minor inefficiencies, such as prop cavitation losses, but these are usually a small enough factor to ignore.

So you've got the interplay of these four inefficiencies, and if you plot them out you'll see that there are two efficiency maximums where the curves intersect: One for non-planing speed at about 4 knots and another one for planing speed around 14 knots, although the planing speed efficiency maximum is obviously less efficient that the non-planing one. On a MacGregor, the planing efficiency maximum will never be better than the non-planing maximum, so low speed is always more efficient. However, for a perfect planing hull, the planing efficiency maximum will be better than the displacement maximum at lower planing speeds, simply because the pure planing hull will have higher displacement drag when not planing than a Mac and lower laminar drag while planing (although aerodynamic drag begins to dominate the equation around 60 knots).

The four knot efficiency maximum is only slightly higher than the "steerageway minimum" of 3 knots on a Mac. Below three knots there is not enough water motion across the daggerboard and rudders to provide the lift force necessary to keep the boat moving straight against any kind of other force (windage or current), and so the boat will only track straight in a dead calm. This is the concept of minimum steerageway speed. On a small boat with a big motor like a Mac, the parasitic engine loss is still too high at 3 knots to be maximally efficient--this is NOT the case if you have a smaller motor (<20 hp), in which case minimum steerageway IS your most efficient speed.

The minimum clutch speed is simply the lowest speed the boat will go at idle with the forward gear engaged and the prop rotating, which on a Mac is lower than minimum steerageway (it's about 1.5 knots on my ETEC) but on large seagoing vessels it's likely higher than minimum steerageway. Minimum clutch speeds only apply to internal combustion drives (diesel, gas, and gas turbines) that have 0 torque at 0 RPM. Motors that have maximum torque at 0 RPM (steam turbines, nuclear, and electric drive) do not have a minimum clutch speed and can rotate the prop as slowly as they want. These boats can operate well enough at low speed to dock themselves often times, whereas the minimum clutch speed affected drives usually require tugs or power thrusters to dock themselves.

The least efficient speed, which is actually the most important number to know, is at 9 knots on my boat. This is the speed at which you have maximum displacement drag AND maximum laminar flow drag because the boat has not yet lifted out of the water on a plane. Parasitic engine loss and aerodynamic drag are not significant components, but displacement drag dominates. This is also the speed at which the control surfaces from displacement to planing (daggerboard and rudders) generate considerable drag and the speed at which the boat's mechanism of control switches from rotating about the CE to planing on the flat stern, thus creating a zone of instability (7 .. 11 knots) during which region the boat will oscillate between rolling into a curve from planing and rolling out of a curve from turning. For the control oscillation and inefficiency reasons, you should power through this region as quickly as possible while going strait and with all boards up.

Make sense?

[mastreb]

Really! I know it sounds silly but think about it! Way down at the end of the daggerboard just have about bottom aft 12 inches of the daggerboard able to articulate about 2 or 3 inches of trim. You know, ilke cut a little 3 inch sliver from the rear of the DB to about 12 inches up from the bottom of the DB? You know? Like an airplane flap or trim tab?? (Am I making any sense?)

BOAT--In fact this will work to reduce heeling, but it increases hydrodynamic drag, which means you pay a price in forward motion. To compensate, you would have to keep more sail out and reef later. You will wind up fighting the heeling force of the wind with increased lift from the daggerboard. This is only going to work well when you have high speed through the water (5+ knots) and low drag component on the sails (i.e., sails in "lift mode" or while pointing) and not in drag mode (i.e., broad reach or running).

In fact daggerboards with trim tabs has been done on race boats, and just as the analysis above predicts, it provides some improvement while pointing, but is of no value on other points of sail.

On boats with wing sails, where the entire sail is rotated so that it always operates in "lift mode" and never in drag mode, a trim tab on the daggerboard will always be optimal. Just like trim tabs on an aircraft are always optimal.

The best way to reduce heeling on points of sail other than pointing is to reef. Lower drag = less heeling. I'm able to maintain a constant optimal 20 degrees of heel by reefing the headsail as appropriate for the point of sail and wind conditions once, and then keeping the mainsheet in hand and loosing it whenever the heel goes higher than desired, or hardening it up when the boat straightens it up. That single mechanism of control has done more to improve my average sailing speed than anything else.

Matt

[K9Kampers]

Okay, so I'm dumb, I'm sorry - I was just thinkin.

Your words, not mine. The part that I thought funny was

...for racing...

. Like putting running shoes on a cow!

Don't let me stand in the way of your creativity. I too am a dreamer, designer and builder of things that both have & have not worked. I think the dagger foil idea has been discussed here before, ya gotta dig into the archives.

For some wild boat shi7, check out the Speed Dream 27