Monday, November 28, 2016

Storm windows? On a boat??

We use Eolian all winter long (at the dock anyway), therefore we heat her all winter long.  On houses, storm windows are used to provide an extra layer of insulation against the winter cold and weather.  If you have ports like these:

Do you have ports like this? can easily make and fit storm windows for them too!  I  don't take credit for this idea - it came from Drew, 6 years ago.  

But in any case, it couldn't be simpler.  First you need to remove the screens from your ports (we don't have ours installed - no bugs to speak of in the PNW... :^) ).   It is easy to do this.  The rubber gasket that traps the screens in place is not glued in - it is just wedged into a slot on the port frame:

Just pull it out
You just need to pull it out.  If you haven't ever had yours off, they may be glued in there with algae and other growth tho.  With the gasket off, simply lift the screen out of its recess.

Of course, you'll need the actual storm windows.  For these you'll want some kind of thin plastic - less than 1/8" (the thickness of the screens).  I made mine out of the glazing from a couple of old poster frames that were destined for the recycle bin.  I just traced the outline of the screen on the plastic sheet and then cut them out on my bandsaw.  I suppose you could use a sabre saw, or even a hack saw (tho the corners would be tedious).  And you might even want to smooth out the edges with a bench grinder and/or a file - I did this with mine.

And just slip them in where the screens were

And then you just drop them into the recess that the screen was in, and reinstall the rubber gasket.  (If you look closely, you'll notice that there is a joint on the gasket - this should go to the top.)  Be sure to get the gasket flange firmly pushed into the slot all the way around, otherwise the window won't close - you could break it if you try.

Easy peasy.


Monday, November 21, 2016

Blogging to meet people

Those of you who have been blogging for a while (we'll hit 1000 posts sometime in 2017) know that a blog is a wonderful way to meet folks.

On a rare occasion, the meeting comes not in the bloggosphere, but in person - these are most special!

And this weekend, it happened again.  We met Jonathan and Sarah, the brand new owners of s/v Odyssey, a beautifully maintained and fitted out Baba 35...  that was coincidentally for sale right here in the Cap Sante marina.  Jonathan & Sarah are from Oregon, and have both apparently been readers of this blog for some time, so when they found themselves headed to Anacortes, they contacted us and arranged a meeting...  a meeting that lasted 4 hours aboard both Eolian and Odyssey, included wine and champagne (!) and a wonderful from-scratch carrot cake that Sarah had baked aboard.  And it turns out that we have way more in common than we could possibly cover in that short time, so I'm sure that this was only the first of many cozy times aboard one or the other boat.  Because Odyssey is going to stay in Anacortes to serve as their platform to explore the San Juans and the Inside Passage....

It turns out that Jonathan is also a blogger (I didn't know!) - you'll want to read the story of the journey that took them to Anacortes and Odyssey.  There's always a story about how the boat picks you...

So the moral of this blog post is:  Blog!  Write!   Look for opportunities to meet your fellow bloggers... don't be shy!   Something wonderful could happen...


Friday, November 18, 2016

Anacortes Haulout?

We will need to do a haulout for bottom paint this spring, and I was wondering if any of the readers would have a recommendation for a place here in Anacortes?  We were thinking of Marine Servicenter...

Monday, November 14, 2016

Random Propeller Thoughts

Eolian's low aspect ratio propeller

I've been thinking about propellers lately.  A lot.

No, I can't explain that.  Perhaps it is a residue of our recent election.  Or something.


Now, I am not a trained Naval Architect.  But still, I have thoughts which seem coherent (to me at least, but then the judge may be biased), some brought on by casual observation of a rooster tail following a heavy cruiser.  Even riding on a ferry you can see evidence of a jet of water that eventually surfaces astern.

To me, the whole idea of thinking of a propeller as a water screw is, well, screwed.

Imagine that the that theoretical speed of a boat which would be determined only by the pitch of the prop and its RPM is called St.  In the common parlance, "slippage" - that condition when the boat is moving at less than St, is considered to be an inefficiency.

But imagine that a boat is moving thru the water at exactly St...  there is zero "slippage" - the prop is a perfect screw.  But then the only force on the prop is drag, as it completes its revolutions thru the water.  So how then is any force created* to move the boat forward?

How about this instead:  Newton's Third  Law:  For every action there is an equal and opposite reaction.  Imagine now that the prop's mission in life is to throw as much water astern as it can...  in a sense the boat becomes a rocket, propelled by the water being thrown away aft.  This theory would have as a consequence that "slippage" is required for propulsion.  If the boat reaches St, from the boat's perspective NO water is being thrown aft... NO propulsion.  This also says that a boat will never reach St, because the closer it gets, the less propulsive force is available - a hydraulic version of Zeno's Paradox.

Given a fixed amount of horsepower applied to the shaft, the product of the amount of water discharged and its speed are fixed.  If you want more water discharged, then for a fixed amount of horsepower input, the discharge speed of the water must be decreased.  And vice versa.  So, if you want a high speed discharge jet (high St), you must compromise with less water in the jet.  Therefore, assuming the same Chevy V8 engine, installed in a high-speed racing hydrofoil, you'll need a comparatively small diameter prop with a HUGE pitch.  With that same engine in a tug, a large, slow-turning prop will give you humongous thrust, but with the compromise of a low top speed.  Variable pitch props do not solve the problem because they only allow their pitch to be changed, not their diameter.

What do you need for your boat?  I bet that you want the most speed you can get.  So:  the highest pitch prop that still provides sufficient thrust to get you somewhere near St for that pitch.  Still a guessing game, tho empirical formulae do exist.

*I said that at St there would be no thrust.  That is not (at least theoretically) true.  Since the beginning of flight, aircraft propeller blades have had an airfoil cross section.  That is, they are really rotating wings, not only generating thrust by virtue of their pitch, but also using the pressure differential the airfoil creates between the front of the prop blades and the rear: lift.  An aircraft propeller, even operating at (or above!) St still delivers thrust because of this.  It strikes me that there is a lot of room for hydrodynamic improvement in water propellers, specifically in improving their lift/drag ratios.  Aircraft wings and propellers (and sailboat keels!) long ago gave up the low aspect ratio shape that today's boat propellers still retain.  Continuing with that thought, boat propellers, it would seem to me, would be well served if they moved toward narrow high aspect ratio blades with a cross sectional shape derived from hydrofoils.  Another trade-off:  enough "meat" will need to be retained in those thin blades to handle the thrust forces...

Related Posts Plugin for WordPress, Blogger...