Weird?!? Trailer hitch ball install causes a drop in MPG's?

[CapnK]

I put a 3/4" receiver hitch on my car a few months ago. Yesterday & for the first time, I put the actual ball mount and ball on/into it.

Here's the kicker: I checked my mileage yesterday afterwards, and was getting a nice 27 mpg's.
  

But then today, that figure *dropped*, big time - down to just 21 mpg's.
  

Aargh!!!

Maybe Brennan has an idea why this would happen...?

[CapnK]

Oh - another detail - I did notice that today, I was being followed. Everywhere I went.

All day, across 3 states even.

No - I don't think it was the cops.

I did manage to get a pic of the guilty party.

[CapnK]

She's a '92. This is the second time she's ever been trailered. Hasn't touched water in ~25 years, been hanging in a lift under a roofed dock the whole time, which explains the chalk. Otherwise, sails and etc are all in great shape.

The Great Rubbing begins tomorrow...

You cannot view this attachment.

[Krusen]

Nice looking little boat!

Good test of the bearings and tires, too.  No cops stopped you to admire your new catch?  They all must have bad eyes.

The boat looks vaguely familiar, but no answer comes up.  What is she?

[CapnK]

American 14.6 - for info/specs see:
https://americansail.com/products/boats/american-146
https://sailboatdata.com/sailboat/american-146/

She's no race boat, but that's not what I was looking for. Thinking more along the lines of 'dinghy cruising'.

I jacked her up and checked both tires for rolling resistance and grease quality before heading home. Added some grease, made multiple frequent checks the first couple hours to make sure all was well. Never got over slightly warm, despite being only 8" and running at 70mph on occasion, 60mph pretty much sustained for 4 of the ~6 hours.

My one brain fog was the trailer lighting. SC laws being what they are (lax), and that I rarely trailer, I didn't even consider that in my preps. Doh! I used some "hacks" to make it OK WRT safety and to avoid the attention of any po-po.

[Captain Kidd]

Well, that explains the drop in mpg! LOL

Nice find! Hopefully I'll be telling the same story soon. Waiting for the weather to break a bit and then I'll have a 1400 mile round tripper to pick up a new-to-me boat.

[Charles Brennan]

Kurt, Not all that remarkable.  It would easier to explain with more data. 
You may be coming down with Timm R. Syndrome: Telling us HALF of what we need to know! 

Starting with the tow vehicle: 4, 6, or 8 cylinders? 
From the pic, looks like it might be a 4 cylinder.  The more ponies under the hood, the less mpg are affected by weight. OTOH, the poorer the mileage is, to begin with.
In general, the automotive industry assumes 1% - 2% per 100 lbs of weight aboard a vehicle, depending on hp. (cylinders).  That jumps to 2% - 5% per 100 lbs for trailered loads, again with the smallest motors being the most affected.

When I first purchased Urchin, I also had a 19 foot power boat, a bow rider with a prominently flared bow for a dryer ride.  It cost me 5 mpg when I towed it with my International Harvester Scout II, with a 345 hp V-8. I was surprised to see that Urchin only cost me 3 mpg when I towed her, even though she was 300 lbs heavier than the power boat.  I realized the more streamlined shape of the sailboat hull in the "wind shadow" of the vehicle was influencing my mileage.
So it's not just weight, but cross section in the wind stream that affects mileage.

So let's look at your tow rig.
27 mpg, dropping to 21 mpg, while towing the sailboat.  Published specs on the American 14.6 are 340lb. 
Since you DIDN'T GIVE US A WEIGHT SLIP VALUE!!     (If ya can put a number on it . . . . )
For the whole rig, so we'll have to make up numbers from whole cloth, but the closest we can get is a Continental trailer being about 350 lbs for trailers in your general size range.
Let's assume 10 lbs of glop on board, just to round the numbers up to 700 lbs for boat and trailer, for easier arithmetic.   

At the low end of the estimate (2% per 100 lb X 700 lbs) 14% of 27 mpg would be 3.78 mpg, dropping the mileage to 23.22 mpg.
At the high end of 5% per 100 lb X 700 lbs, 35% of 27 mpg would be 9.45 mpg, dropping the mileage to 17.55 mpg!    
Your reported mileage drop of 6 mpg works out to 22%, which divided by 7, gives us 3% mileage drop per 100 lb, or very close to manufacturer estimates.
Arithmetic WORKS!! 
Who'da Thunk It?!? 

Kinda hard to tell from the pic, since the trailer may be disconnected and the vehicle is in the background. But I would start with the rig hitched up and in a straight line and then stand well in front of the vehicle and sight down the length.
How much of the sailboat hull is sticking up past the slipstream of the tow vehicle? 
Something as simple as lowering the trailer ball mount height might buy you 1 or 2 mpg.
The other thing that the manufacturers point out, is that there is a (slightly) lesser penalty per 100 lb, for stuff in the trunk, than there is for stuff in the boat  trailer.

Hope this helps,
Charles Brennan

[Wolverine]

Small sailboats are like puppies. They tend to follow us home.

Congratulations on the new "puppy".

[Captain Kidd]

Looks like a Marquis or Crown Vic. I've had 3 of the Mercs and got about 27 on the road with all of them. 4.6 V8s. My 6 cyl Kia got 21-22 hwy and can't remember towing. I do remember my 6 cyl Trailblazer getting 21 hwy and 13 towing the Hunter! Sheesh - talking about taking a hit!

Assuming my deal goes through with the Hunter 19, I'll have ample time to check mpg - 1400 miles. That Hunter 19 will catch a lot of wind I believe.

[Riley Smith]

Oh, the ball must create turbulence on the trailing edge of your ride.

I love the boat. Lots of room in that hull for bodies and stuff! I have a decided negative attitude about cabins on boats less than about 18-20 ft long. It is a huge waste of space IMHO and forces compromises for situations that occur much more frequently than actually USING the cabin. The cabin on the old Victoria was absolutely claustrophobic. The catboat was much bigger despite being EIGHT FEET SHORTER. Apples and oranges I know but you can sort of understand.

[Timm R Oday25]

Charles as much as I like being an example ,heck even a bad one. Would his mileage increase with bigger tires offering less rolling resistance ?

[Charles Brennan]

Timm, I hope you know my jests are made with affection. (Although you DO make me crazy, sometimes!) 
I am certainly not a fan of 8" wheels on trailers. As you may (or may not!)    remember from my long-ago article on trailer bearings, an 8" wheel is rotating at over 1400 RPM at 70 mph.
Certainly tire resistance is one of the factors that automotive manufacturers use in their calculations, but so is weight and trailer windage; with weight having the most uhhh . . . . . weight in their calculations.
Which brings us to a nature vs nurture type of argument:
Would the added height of the wheels increase the windage slip stream surface area behind the tow vehicle, thus offsetting the advantage of the lowered road resistance?   

An interesting thing to ponder in the winter months.

Food for thought,
Charles Brennan

[Frank B.]

I think the mfg's numbers are maybe simplistic, straight linear rather than a curve.  I also think they may not fully take into account Newton's first law with regard to inertia. 

My sailboat tow is 4500 - 5000 lbs.  Never weighed but a good estimate. At the low end of the mfg. range seems like I would have a 90% impact on my mileage, on the high end of the range I would be in negative territory. 

The reality is that the Tacoma truck 4.0 six gets about 21-22 in the best speed vs MPG place that is 2000 RPM which gets me about 68 MPH.  With that 4500 lb. tow it drops to about 14 mpg running at the same 68 MPH.

Have I left something out of the math here? It is early morning and I'm not through my coffee yet.

However, the truck stays, eighteen years old and the best I've ever had.  Best mileage highway, no tow, is 23 MPG which is at 55 MPH tested on the Natchez Trace many times.  Now while that isn't great for a midsize truck, it only drops to 19.5-20 around town which is fabulous for a truck of that weight.  Even plan to spend some "vanity" money on it this year, since I've never had to spend any non-discretionary money.  Clear coat is finally stripping off, so it will get a paint job.

BTW the math works just right pulling a 1000 lb tow with a 2016 Subaru outback.You cannot view this attachment.

[Norm L.]

Love the photo and love the Trace.
Last week I found some old photos from a 3-day cancer donation camping ride on the Trace. When I have had a job on the Mississippi River in the general area of Natchez I have lengthened my drive home via a section of the Trace.
Of course, much smoother and scenic than when created.

[pgandw]

Windage is everything at higher tow speeds.  Weight is slightly linear, but wind resistance goes up with the square of the speed.  If you double your speed from 30mph to 60mph, wind resistance quadruples at 60 compared to 30.  The resistance from weight might have gone up by 10% by doubling the speed, if that.

Where this falls apart is towing over hills.  Wind resistance stays the same if speed stays the same, but weight resistance is increased going upgrade.  And no, you only make it up partially going downgrade.

Fred W