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BRS17 Information


btrowe

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btrowe,

 

if there's 10 hp outboard envisaged (and you need a long shaft one for BRS 17) , make your transom doubled with a solid wood board above the aft deck. And never tow the boat with the outboard left on the transom. Otherwise you're at risk of breaking the transom. 

 

As for the knee, it is exposed in BRS 15 plans indeed, but Graham did not used it in BRS17 design. 

 

If you prefer (or already have ) a short shaft engine, there're few systems for mounting it outside.

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Wwbaginski:  On my 15's plans, it specifies a deep notch in the transom.  This notch accommodates my short-shaft 5 hp motor, getting the cavitation plate well into the water.

 

Btrowe:  Wwbaginski's concern is well-founded.  The cavitation plate on your outboard will need to be submerged.  If you already have the motor, make sure that your transom height matches your shaft length.  You can see the difference in transoms between his 17 and my 15.  The 17's transom may certainly be notched like mine, to accept a short-shaft motor without an external bracket.  Just make sure to modify the rudder accordingly.  If you haven't purchased the motor yet, the choice is yours to make.

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The BRS17 plans have the notch like yours Don. I don't have a motor yet so it's good to know that a short shaft should work. The motor will be clamped on the transom, definately don't want it catilevered out any further aft than necessary. In sail mode the outboard would be left ashore and oars or a small electric motor would be used. I will add a knee from transom to keel and also where the tramsom meets the gunwales. I find the aft corner reinforcements a great place for tying off and as handholds.

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Those are different transoms and different notches. It is stated at the BRS17 plans "Transom is designed for long shaft outboard". A short shaft will work only if you re-design the transom and/or the notch enough to get what Thrillsbe says - the right position of the cavitation plate when submerged.  

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1'' below the bottom is about right for a powerboat, but probably way too little for a sailboat. Several reasons for this.                                                                                                                           1. Where the motor is mounted off center, the bottom is usually above the waterline.                                                                                                                                                           2. Moving forward in the boat will raise the transom.                                                                                                                                                                                                             3. Heeling the boat will raise or lower the motor.                                                                                                                                                                                                                     4. Wave action can "rock" the boat, lifting the motor.

 

Maybe some of you guys have more experience with this, and have come up with a good height for the BRS-15, CS-17, or CS-20.

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Thanks wwbaginski, I found the detail in the plans. It is indeed 19.5" from cutout to keel so a long shaft is needed. I wouldnt want to lower the transom. Drawing of DWL shows 14" to cutout which I'm comfortable with in the waters Ill be in.

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1'' below the bottom is about right for a powerboat, but probably way too little for a sailboat.                                                                                                                                                                                            

Chick, I'm  reffering to btrowe's plan of using  BRS 17 as a powerboat with 10 hp motor on the center of the transom.  

 

Of course It might be interesting to discuss  small sailboats with small outboards mounted off the centerline, but this topic is titled "BRS17 information" and less people seem to be interested in. So may be it would be useful to start another topic?

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The discussion about motor boats is relevent since that is what the boat is when configured with an outboard. The motor will be clamped to the centre of the transom and will be at the recommended depth below the keel. This confirms that no changes are required. I just have to get a long shaft motor and everything should land in the right spot.

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I ran a short shaft motor on my (very) notched transom last summer.  I had no problem with it.  I'm sure that if I walked forward to weigh anchor it would have gurgled.  I like the 1" guideline for motors mounted on the centerline of the boat.  I wonder what it should be off the centerline.

 

wwbaginski:  We often veer off course on these discussion threads-- much more than this, too, I might add.  We always seem to find it back to home port, so not harm is done.  Don't abandon ship!

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Just confirming your intended use for the boat. Like Thrillsbe, sometimes you will be configured as a sailboat, and other times as a powerboat. In powerboat mode, you want to carry 3-4 adults. The reasoning for the 10 hp motor is to handle that load.

 

Sounds reasonable as long as you don't intend for the boat to plane the same way as a straight bottom of an actual power boat would. The rocker bottom  will plane to some degree, and exceed "hull speed", but as power is added, the bow will want to rise, and the boat will "suck" down into a "hole" that it "digs" for itself. The increasing drag will limit your speed. That being understood, all should work out well. We'll look forward to following your build.

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That's right Chick. Different configurations different days. I like fishing and sailing and have room in the driveway for one boat ;)

It will likely only see freshwater lakes and rivers, although I like the idea of sailing to Key West one day... we'll see.

I've had great feedback from Don and the BRS15 he build has really inspired me. He is using a 6hp on that, and I think the 10hp would likely suit the BRS17 best for the load intended.

When I get to putting her in the water I'm sure I'll play with the different size motors to find the sweet spot.

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After reading more about wood use I'm debating my selection of ash for the stem. My resoning is if the bow gets dinged or rubbed, water might get to the wood, and ash doesn't do well if exposed to water. For the BRS the stem is made of 2 laminations of 3/4" lumber and there is no curve in the stem. I'm thinking white oak or douglas fir might be better here for rot resistance, and also I'm not sure of the best orientation of the grain... would flat sawn or quarter sawn be best?

 

1) plan view flat sawn:

 

     stem cap

 =========

//========\\  <---hull side

        stem

 

2)  plan view quarter sawn:

 

   stem cap

  |||||||||||||||||

//|||||||||||||||||\\  <---hull side

      stem

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I agree.  Plus, I've heard that white oak does not bond as well with epoxy, long-term.  In fact, System Three has come out with a special formulation of resin for dealing with this and other oily/waxy woods.  I found this out too late-- my stem and keel batten are both of white oak.  I did back up their attachment with a few screws.  Fir is great for that.  So is "lumberyard pine"-- that's the select stuff you'll find at your big-box lumberyard.  I didn't use any, but most B and B builders use nothing but this wood.

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It's interesting that System Three has a special formulation for the "whites" yet tests have proven (many done by West System) that it's simply surface prep that gets the whites to bond well, long term. Last year, I had the pleasure of seeing a boat I restored many years ago. It was a 26' lapstrake power cruiser, built in the traditional fashion and clenched. It was back in the yard because of damage and the yard that normally works on his boat (mostly engine and maintenance stuff) wouldn't touch it, because I'd used machine screws to fasten the laps, which they thought was nuts.

 

In any case, I repaired and/or replace all but a handful of these dainty, closely spaced white oak frames, knowing each one well. This boat was built before the manufacture elected to use goo in the lap seams, but I did use polysulfide, during replanking. The now 15 year old white oak laminated frames and repairs, where pretty much as they were the day they left the shop. A few under the engine had some oil fouling, but no gaps or voids could be seen in the lamination stacks and fasteners look just fine as well. In fact, I didn't clip off the ends of many of the machine screws, in the out of the way places in the bilge, when I sent this boat home with her owner, but I did clip off the ones that remained, finally finishing her up, I guess.

 

The oak prep, which is essentially the same as any of the "oily wood" treatments, is a chemical bath and scrub down, before epoxy goes on. It removes the tannins and oils in the wood, flashes off, leaving empty and naked wood cells, to get filled by goo. I've bonded teak with this same technique and it works just fine, just as the testing has shown, though (again) I find it interesting that System Three needs a special formulation. I'd be interested in seeing the MDS on that batch. I guess just one more product "solution" for another perceived issue, they can market. I wonder if they use reactive diluents, etc., etc., etc. to answer this perception.

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