Author Topic: 28 GA in Pagosa Springs colorado  (Read 16926 times)

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Dan Boccia

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Re: 28 GA in Pagosa Springs colorado
« Reply #375 on: July 23, 2020, 06:53:54 PM »
In Anchorage, the best companies for stainless steel railing are the larger mechanical contractors who get into stainless piping on larger commercial/hospital/brewery, etc. jobs, so I would call around to see if any of them are game to do it - their welders have to be certified to higher standards than most boat building outfits and their jobs look awesome!

Djeffrey

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Re: 28 GA in Pagosa Springs colorado
« Reply #376 on: July 30, 2020, 08:26:13 AM »
More sea trials today. I find myself in the same position at Dan B . I need to raise my engine a couple inches. My cavitation plate is to low. Will be raising it today. Dealing with my self loathing that I cut off the top of my transom, oh well Ill get over it. I also need to go down in prop pitch, at full throttle and a 15 pitch prop I am at 5000 rpm. Meaning I am leaving up to 1000 rpm on the table. Going to start by raising the engine and then move onto the prop. I feel I will gain some RPMs by raising the engine. I was always under the impression that it was better to have the engine to low then to high, I now believe its better to be high and work down. In driving the boat for several hours I find that at 3000 RPMs the low cavitation plate is pulling the back of the boat down, at 3200-3500 it pops up. I also find that when I am at full throttle and try to trim the motor it pulls the boat down.  Dan b video posts are  great and help me understand my real life experiences.

Dan Boccia

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Re: 28 GA in Pagosa Springs colorado
« Reply #377 on: July 30, 2020, 10:49:10 AM »
I concur with your findings and your approach. I just got back from a fishing trip and again had improper conditions to be hanging out the back trying to video, but I did go back and look while a buddy was running the boat and the anti-cav plate always seemed just a bit out of the water, just perfect as far as I can tell. Go up two holes and let us know how it looks!

Brian.Dixon

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Re: 28 GA in Pagosa Springs colorado
« Reply #378 on: July 30, 2020, 01:47:46 PM »

I like the approach of starting too high then working down.  Unfortunately, it's common in Alaska to hear the suggestion that the cav plate should be 3/4" under water or so.  But that's typical for a work boat, not so much a sport boat.  The Great Alaskan is light enough, regardless of what you use it for, to justify more of a sport boat tuning of the motor height.  The risk of cavitation occuring on a hard hole shot is low, so why not?  You'll get better efficiency, and I suspect we'll hear from Dan on, with the cav plate higher ... less drag AND the line of thrust being higher on a planing hull makes it more efficient.

bd

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Djeffrey

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Re: 28 GA in Pagosa Springs colorado
« Reply #379 on: August 04, 2020, 06:10:05 PM »
Day three on the water. Raised the motor 2 inches, gained 500 RPM, way more then expected. Up to 5500 RPMs and happy with that at 7000 feet elevation. Last week I felt like the the back of the boat was pulling down, it was. I was getting water in through my scuppers when I would turn. Today no water in the scuppers. 37 MPH. More then I need most of the time.

Dan Boccia

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Re: 28 GA in Pagosa Springs colorado
« Reply #380 on: August 04, 2020, 06:20:29 PM »
Wow! Going up 2 holes gained you 500 rpm? That's more than I would have thought too! I would say you've got the engine height set about right and the prop is just about right, congratulations! That must feel good.

Djeffrey

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Re: 28 GA in Pagosa Springs colorado
« Reply #381 on: August 04, 2020, 07:33:02 PM »
I forgot to mention that two hundred of that RPM came from trimming the engine up

Brian.Dixon

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Re: 28 GA in Pagosa Springs colorado
« Reply #382 on: August 05, 2020, 06:30:17 AM »
Day three on the water. Raised the motor 2 inches, gained 500 RPM, way more then expected. Up to 5500 RPMs and happy with that at 7000 feet elevation. Last week I felt like the the back of the boat was pulling down, it was. I was getting water in through my scuppers when I would turn. Today no water in the scuppers. 37 MPH. More then I need most of the time.

Yup ... all boats are a teeter totter around the center of gravity.  Trim the bow up and the stern goes down and vice versa.  If the motor is too deep in the water, then you've got an undesired trimming up of the bow ... Note that when a boat is on plane, the center of gravity is above the waterline (around 9" to 12" in a Great Alaskan).  In an ideal world, you'd have the line of thrust (prop) at the same height as the center of gravity, but that's impossible when on plane.  The deeper the motor, the more leverage the motor has on boat trim.  The higher you can run the motor, the better ... as long as you are getting cooling water pick-up in all conditions and operations (hard turns) and your prop is not cavitating (including jamming the throttle on slow speed hard turns - aka 'evasive maneuvers' when you need that thrust!).

Brian

The Great Alaskan - Professional grade offshore performance - Designed to be built by anyone! - https://www.glacierboats.com  ><((((> .`.><((((> .`.><((((> .`.><((((>