GS 28 - Behavior at High Speed

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fallguy1000
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Re: GS 28 - Behavior at High Speed

Post by fallguy1000 »

Johnston wrote: Fri Jan 21, 2022 2:07 am This is understood. Is it possible to give a speed estimate for a single 300 HP … that I believe would be within design limits?
Open a new thread. TomW will be able to estimate the prop and speed using design weights. Fudge weights high by 800 pounds of people.
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Re: GS 28 - Behavior at High Speed

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BarraMan wrote: Fri Jan 21, 2022 7:50 am
Johnston wrote: Fri Jan 21, 2022 2:07 am This is understood. Is it possible to give a speed estimate for a single 300 HP … that I believe would be within design limits?
How fast will a GS28 go wil 300 ponies on the back?
I’ll venture an answer - fast enough! :lol:

How do I know? :doh:

Cause the recommended max hp for my Hull is 250, I upscaled it 10% but still put 250 on the back.

It’s a big boat (22 ft) and built like a tank! It’s not prop’d for speed - but will nudge 50 kts (call it 60 mph). :help:

Now that I have built it and driven it a lot, I know it would handle 300+ hp with ease - but why? It is nice, comfortable and safe at 25 - 30 kts, sometimes 35 kts, occasionally 40 kts!

Why would I want to do 50 kts and burn 3x the gas I do at 25 kts - it’s a fishing boat ! 8O
I like this response … the answer to your question about why is “because you can”!! 😂😂
Last edited by Johnston on Fri Jan 21, 2022 4:21 pm, edited 1 time in total.

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Re: GS 28 - Behavior at High Speed

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fallguy1000 wrote: Fri Jan 21, 2022 9:04 am
Johnston wrote: Fri Jan 21, 2022 2:07 am This is understood. Is it possible to give a speed estimate for a single 300 HP … that I believe would be within design limits?
Open a new thread. TomW will be able to estimate the prop and speed using design weights. Fudge weights high by 800 pounds of people.
Why open a new thread? This was one of my first questions before it was derailed by a side lecture on weight, balance, how hulls are built for what they are designed for etc etc etc … and now you tell me to open a new thread for the simple question of what speed can this boat do with its DESIGNED and specified max horsepower of 300 if built as designed and specified… 🤷?

I promise to open a new thread if you promise to let someone else answer my speed question?! Deal?!

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Re: GS 28 - Behavior at High Speed

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Only so TomW sees it.

His ears will perk up for speed and prop calculations.

He has not posted to this thread is all.
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Re: GS 28 - Behavior at High Speed

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Johnston Tom here be glad to help you on estimated speed and estimated prop size. I assume all these will be estimates so do your best. I really like the GS28.

Weight of the boat as built including console. Add any accessories like a T-top. I found that the base hull is 2000lbs, so that is everything up to the deck, it does not include paint or any finishing or console. Just wood and fiberglass. It does not include any options you make like the jump cabin.
Which motor are you putting on it? I will get the weight from Manufacturer specs. Let me also know the year.
Amount of gas you will carry when leaving the dock.
Gear, this is all the cables, controls steering gear, wiring and lighting, etc., hardware, fuel tank and lines and other miscellaneous hardware. For a large boat like the GS28 I use a 300lb constant. Add more if you think it is more.
Number of people and weight
Will you have a live/bait well if so, how many gallons?
Finally, all the stuff you drag on board when you board for a day's fishing, coolers, ice, fishing gear, tackle boxes, safety jackets, food, beverages, ice, bait. I usually estimate 150lbs, but it can add up fast depending on how much ice you bring, size of coolers amount of bait.

Any speed calculation is weight dependent so be as accurate as possible in your estimate. Take your time and be as accurate as possible, it is an estimate after all. I'm retired so I'll be here when you're ready.

Tom
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Re: GS 28 - Behavior at High Speed

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I like this response … the answer to your question about why is “because you can”!! 😂
..... and I like that answer! :lol:

Haha! Trust me - I get it! :lol: I was just trying to show a level of common sense appropriate for my age! 8O

In the places I fish, I have yet to meet another boat that can go around me - and I'm in the fortunate position to be able to afford to burn 25 US gal/hr occassionally ! :D

My fishing buddies know what is going to happen when we are cruising along at 25 - 30 kts and they see another boat approaching us from behind! :help:

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Re: GS 28 - Behavior at High Speed

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Johnston I can also run the GS28 through the calculators assuming weights of 4000, 4500, 5000 and 5500 pounds if you want me to instead of your messing with coming up with numbers. But do let me know what motor you are considering as that does affect the speed part of the calc. I just ran it at 5000lbs with a Yamaha 300 which has a final gear ratio of 1.75 and came up with a top speed in the very high 40's touching 50. Again, this is in perfect seas. i am not sure I would run it that fast based on Jacques comments, and I would definitely want trin tabs.

Tom
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Re: GS 28 - Behavior at High Speed

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TomW1 wrote: Sat Jan 22, 2022 3:44 pm Johnston I can also run the GS28 through the calculators assuming weights of 4000, 4500, 5000 and 5500 pounds if you want me to instead of your messing with coming up with numbers. But do let me know what motor you are considering as that does affect the speed part of the calc. I just ran it at 5000lbs with a Yamaha 300 which has a final gear ratio of 1.75 and came up with a top speed in the very high 40's touching 50. Again, this is in perfect seas. i am not sure I would run it that fast based on Jacques comments, and I would definitely want trin tabs.

Tom
Thank you Tom - this is very kind of you. Whilst this is still a theoretical exercise at present, this is exactly what I am after.

Are your speeds in mph?

A Yamaha 300 would work fine for my needs.

I would be curious what the designer has to say about those speeds …. 300 HP is the max allowed per the study plans, so hopefully it would be ok!

One question I have for him is whether with a sharp forefoot and a flat aft section there is a risk at high speeds of the bow veering off to the side .

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Re: GS 28 - Behavior at High Speed

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Johnston wrote: Mon Jan 24, 2022 2:08 pm
TomW1 wrote: Sat Jan 22, 2022 3:44 pm Johnston I can also run the GS28 through the calculators assuming weights of 4000, 4500, 5000 and 5500 pounds if you want me to instead of your messing with coming up with numbers. But do let me know what motor you are considering as that does affect the speed part of the calc. I just ran it at 5000lbs with a Yamaha 300 which has a final gear ratio of 1.75 and came up with a top speed in the very high 40's touching 50. Again, this is in perfect seas. i am not sure I would run it that fast based on Jacques comments, and I would definitely want trin tabs.

Tom
Thank you Tom - this is very kind of you. Whilst this is still a theoretical exercise at present, this is exactly what I am after.

Are your speeds in mph?

A Yamaha 300 would work fine for my needs.

I would be curious what the designer has to say about those speeds …. 300 HP is the max allowed per the study plans, so hopefully it would be ok!

One question I have for him is whether with a sharp forefoot and a flat aft section there is a risk at high speeds of the bow veering off to the side .
Yes, my speed is in mph or 43.5knts. Jacques and I are always within a couple of mph of each other when calculating speed as we use similar calculators. You will also be attaching a skeg to the bottom of the boat from about 18" from the transom to about 12' from that point. This will be a 2x2 attached to the hull. I would also recommend a 4-blade prop as it will help in straight line steering and handling in rough waters.

One other thing to note is that that this is not a flat bottom boat. It has a dead rise at the transom of 8 degrees and the skeg will help with tracking.

Ask if you have any questions please ask. Where are you located by the way?

Tom
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Re: GS 28 - Behavior at High Speed

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Should power slide nicely! :lol:

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