Author Topic: New bow thruster solutions  (Read 5624 times)

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Brian.Dixon

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New bow thruster solutions
« on: April 19, 2019, 09:52:10 AM »
FYI - At one point in time, I stated that bow thrusters might not work on the Great Alaskan - the ones that have a horizontal tube through the bow (impeller inside) were for the most part too large to fit this non-deep-V style of hull.  But I have more recently discovered that there are both compact bow thrusters that may fit and at least one that uses jetted water through a couple of nozzles (port and starboard) that definitely will work on a Great Alaskan  In any case, just wanted to correct/update what I said in the past - It appears that we're all in luck now, and just in time for the larger Kodiak model of the Great Alaskan:

  https://www.jetthrusters.com/  Jetted bow thruster - Dutch made, available in the United States - Easy to have both bow and stern thrusters on even a small boat.

If it were me, I'd go with the water jet version ... quiet, no tricky installation near the keel fillet and glass, and can work in a variety of mounting locations, water inlet can be anywhere.

Brian

« Last Edit: April 19, 2019, 09:55:19 AM by Brian.Dixon »
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kennneee

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Re: New bow thruster solutions
« Reply #1 on: April 19, 2019, 10:40:31 AM »
Brian- Looks interesting. Any idea of the cost?
Ken

Jim_Hbar

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Re: New bow thruster solutions
« Reply #2 on: April 19, 2019, 11:49:25 AM »
I see five or six big holes, and a bunch of potential leak points below the water-line..??.  :-\ :o
Imagine how fast you would fill your boat if a line broke or a fitting came loose!

That being said, I've cogitated on a similar system, but using nozzles that would operate on the jet pump injector principle. Similar to the coanda effect used by Dyson blower fans.
Pump higher pressure, lower flow water, and have the pump available for wash-down purposes (and repelling pirates?).

Either way, jets are darn inefficient vs. propellers, but that may not be pertinent in this application.
I concluded that hanging trolling motor over the bow would be the less expensive solution for my potential application - YMMV.

Brian.Dixon

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Re: New bow thruster solutions
« Reply #3 on: April 19, 2019, 06:08:00 PM »
Brian- Looks interesting. Any idea of the cost?
Ken

Probably more than I'd want to pay!  But if I were building a Kodiak 30 and parked it in a slip, I'd be sorely tempted to get the jetted system.... or a couple of strong crew members with boat hooks, whichever is cheaper :)

bd
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Brian.Dixon

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Re: New bow thruster solutions
« Reply #4 on: April 19, 2019, 06:11:19 PM »
I see five or six big holes, and a bunch of potential leak points below the water-line..??.  :-\ :o
Imagine how fast you would fill your boat if a line broke or a fitting came loose!

That being said, I've cogitated on a similar system, but using nozzles that would operate on the jet pump injector principle. Similar to the coanda effect used by Dyson blower fans.
Pump higher pressure, lower flow water, and have the pump available for wash-down purposes (and repelling pirates?).

Either way, jets are darn inefficient vs. propellers, but that may not be pertinent in this application.
I concluded that hanging trolling motor over the bow would be the less expensive solution for my potential application - YMMV.

I thought of that too.  3M 5200, metal nozzles, double clamps, and hose support so no bouncing .... and regular inspection.  Good thing about building your own boat, is that you can take all into consideration and make things easy to reach and maintain.

There is such a thing as a retractable bow thruster too, and there are ones that drop down just like a trolling motor (they're spendy though ... probably high horsepower).

Brian
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Silver_S

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Re: New bow thruster solutions
« Reply #5 on: April 20, 2019, 08:14:53 AM »
I concluded that hanging trolling motor over the bow would be the less expensive solution for my potential application - YMMV.
Jim,
I don't have a Great Alaskan yet, (planning stages) but on my current boat I use an Ulterra trolling motor. My plan was to use it exactly as you describe. It has more than enough power, but it doesn't go into reverse. You turn it 180 degrees for reverse. So it is a variable uni directional bow thruster that I have to go to the bow of the boat to power it on and then come back to the helm to auto deploy. Set the power level you need for cross wind and current then dock the boat. A little too complicated, although functional. Your boat and usage may be different on your boat as you mention.

I am going to get some quotes on the jet pump and a retractable model bow thruster. For me personally, I hate the idea of another item to winterize which the jet pump does require. But a small hole at the very front of the boat does give more leverage to allow a potentially smaller pump compared to a large tube through the bow.

-Steve

Rbob

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Re: New bow thruster solutions
« Reply #6 on: April 20, 2019, 08:50:55 AM »
Brian,

Cant wait to see it:  Kodiak model of the Great Alaskan!

Brian.Dixon

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Re: New bow thruster solutions
« Reply #7 on: April 20, 2019, 09:13:34 AM »
Brian,

Cant wait to see it:  Kodiak model of the Great Alaskan!

Yeah ... the study plans have been updated to include the Kodiak model, and the Kodiak Addendum is now available so people can build one ... I've sold quite a few already and am breathlessly waiting to see who will build the first 30-toot Kodiak!  There are also those who are at a stage where they can convert an regular Great Alaskan build into the Kodiak, although none to 30 feet ... I think 28 feet is the longest of those.  :D

Brian

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kennneee

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Re: New bow thruster solutions
« Reply #8 on: April 20, 2019, 09:20:40 AM »
So, how hard is close quarter maneuvering with a light weight boat like the GA with a pilot house acting as a sail? I have lots of experience with heavy displacement sail boats but none with this kind of boat. Some of the BLuejacket builders have added thrusters after some close quarter pucker incidents. My, soon to be launched Outer Banks 26 will probably be similar in handling and wonder if I should wake up at 3am to figure it out:).

Brian.Dixon

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Re: New bow thruster solutions
« Reply #9 on: April 20, 2019, 10:03:56 AM »
So, how hard is close quarter maneuvering with a light weight boat like the GA with a pilot house acting as a sail? I have lots of experience with heavy displacement sail boats but none with this kind of boat. Some of the BLuejacket builders have added thrusters after some close quarter pucker incidents. My, soon to be launched Outer Banks 26 will probably be similar in handling and wonder if I should wake up at 3am to figure it out:).

Yup ... Consider that the #1 contributor to boat's being efficient or not is boat weight (displacement).  If you want efficiency, then the first thing you look into is how to build a more optimal structure from a mechanical engineering perspective - which is what I've done on the Great Alaskan.  The structure is strong and stiff in exactly the right places for how a boat responds to stress on the water (planing, impact loads when hitting waves, hogging loads when 'balancing' over the top of waves, transom stresses etc).  Of course, the second largest contributor to efficiency is the hull form, and third is drag.  The GA uses a near-prismatic hull form with an optimized aspect ratio, and a reasonably fine entry - not claiming fame for myself here, but the boat is a success because of the work and studies done by Lindsay Lord and Daniel Savitsky, whom I studied extensively on my own in addition to the Westlawn school studies.  The structural details should be attributed to Renn Tolman of Tolman boat fame, and Dave Wright (friend, ex-marine mechanical engineer at Boeing).

In any case, to make a long story short, the Great Alaskan is designed to be efficient so that when the dual-I/O deep V heavies all stay home due to rising gas prices, those of you out there with Great Alaskans will be enjoying time out on the water.  The trade-offs include slightly higher windage issues (your question), and less momentum against waves - which means you may need to slow slightly more than the neighboring SeaSport or Orca when the going gets too rough.  This is why, especially on the larger / wider versions of the Great Alaskan versus tight slips, the idea of having those jet-type bow thrusters would make sense.  Don't buy them if you don't need them, but I've put enough boats into tight slips to know all about the pucker factor concept.  I'd love to have bow thrusters on a 30-foot Kodiak.  Fortunately, the Great Alaskan already has 6'4" headroom inside the pilot house, so there should be no temptation to increase the ceiling height of the pilot house - which would add more windage to the boat.

Brian

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kennneee

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Re: New bow thruster solutions
« Reply #10 on: April 20, 2019, 11:27:25 AM »
Brian- Everything in life has trade offs. Clearly the benefits of the GA design outweigh the the downsides! A lot of the same philosophy went into the design I chose to build.
Since we are on the subject of your design, I want to make another comment.
I started building my Outer Banks before I knew of your design and plan package. I love the boat I am building but it is the first and only one under construction at this point. I have often wished I had the community that you provide here to feed each others enthusiasm and help with details specific to the design. I purchased a set of GA plans sometime ago and have “borrowed” a lot of you ideas and applied them to my project.  The plan package is amazing! I read this site regularly and find it very helpful. So, want to say thanks to you and the rest of the crew for letting me ride along here.
Ken

Brian.Dixon

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Re: New bow thruster solutions
« Reply #11 on: April 20, 2019, 12:07:50 PM »
Thanks, Kenneee ... Realistically, windage should not be a huge problem with the GA.  It's not overly tall and most people load them up pretty good to boot.  Which length Outer Banks are you building?

Brian

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kennneee

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Re: New bow thruster solutions
« Reply #12 on: April 20, 2019, 02:41:01 PM »
Brian- I am building the Outer Banks 26. It isn’t on the BandBYacht design site yet. They show a 20 and 24. I guess I am the beta tester for the 26. Here is a link if anybody want to see the build.
https://goo.gl/photos/42vU3BKQDsnMxbPp9
I haven’t updated it in quite a long time. I took a break from building and did some travel for 5 months and recently returned to get back to work. I am about to start the electrical system and will mount the motor in the next few weeks. Still a million details but I think I may just splash her soon and go for a spin.
Do you recommend trim tabs for you GA? If so, any particular kind? I will probably be asking a lot of these kind of questions since it will be time to buy some of the fun stuff soon. Electronics, etc.
Thanks.
Ken

Jim_Hbar

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Re: New bow thruster solutions
« Reply #13 on: April 21, 2019, 10:25:06 AM »
Ken:

Wonderful build, looking great!

You are quite evidently in the same neck of the woods that I am, with you using a Slegg truck to lift the hull. 
It would appear that I'm 50 km from your location, on Gabe.

kennneee

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Re: New bow thruster solutions
« Reply #14 on: April 21, 2019, 11:31:51 AM »
Jim - I am on Salt Spring. Say hi if you find yourself on the island.
Ken