FS18 OFFSHORE

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OneWayTraffic
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Re: FS18 OFFSHORE

Post by OneWayTraffic »

I really think that much increased sheer will be too unstable. A lot of wind age on a 1.4m wide boat. Stick with minimal increase.

I understand that the appeal of the FS18 is the lower hp requirement but you do have other options all of which would be more capable offshore on a good day. The OB15 will run with a 20hp for example.

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Re: FS18 OFFSHORE

Post by OneWayTraffic »

Or the GV13. More usable room and more stable. 25hp max and 20hp pushes them fine.

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OlivierP
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Re: FS18 OFFSHORE

Post by OlivierP »

A 16 Cape Cod (scaled ?) from Selway Fisher could be a good fit.

Not self bailing though, personally I wouldn't go far offshore on a non self bailing boat - but I know many do.
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pedroe
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Re: FS18 OFFSHORE

Post by pedroe »

TomW1 wrote: Sun Oct 09, 2022 9:33 pm Realize you are raising the Center of Gravity and you should put some weights low in the boat on the centerline. Don't know what the plywood you are adding to the sides of the boat weighs but just put a similar amount of weight along the center spread out from the transom to the bow.

Tom
Hi Tom.

I measured the increased area of the sides in the drawing and it is 1.5m2 per side. For reference 1 single sheet of plywood is 2.8m2.

In conclusion I will have approximately one additional sheet of plywood plus fiber. If I use foam core in this part instead of plywood probably it will help a bit.

Your ideia is good. In order to reduce the additional height of the CG, I could had some weight down bellow. But then I weigh 76kg (167lb), imagine that I weigh 96kg (211lb) with a big beer belly. Wouldn’t that be equivalent to raising the sides regarding the total CG location ?

All I need is a boat that can go offshore 5 miles in calm conditions. Also I will be 5-7miles away from shelter. I will only go offshore with wind around 5-6 knots maximum, but I need a boat that can handle sea conditions if the wind raises to 15knots. By that time I believe I already reached the marina.

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OneWayTraffic
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Re: FS18 OFFSHORE

Post by OneWayTraffic »

What about the LM18? Little wider but still very easily pushed. According to the designer 25hp is more than enough. 20hp would push that fine. I’d increase freeboard at the bow only and 3” scuppers out the back.

pedroe
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Re: FS18 OFFSHORE

Post by pedroe »

OneWayTraffic wrote: Mon Oct 10, 2022 3:01 pm What about the LM18? Little wider but still very easily pushed. According to the designer 25hp is more than enough. 20hp would push that fine. I’d increase freeboard at the bow only and 3” scuppers out the back.

That is an option for sure. I just don’t know how much “safer” would the LM18 be compared with the FS18.

fallguy1000
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Re: FS18 OFFSHORE

Post by fallguy1000 »

You are getting some bad advice.

The designer needs to coin in.

You do not use a 20hp engine and then add a lot of freeboard and mass down low to offset. This is design spiraling out of control.

Build the Panga 20. It is the right boat for the engine constraints you propose.

The FS18 with higher bulwarks is too much boat for the 20hp engine..and higher bulwarks is not something wise as it raises the VCG of the boat. And adding mass down low makes it harder to plane and pos buoyant? Probably not...

One of the guys mentions weather helm. Do you realize higher freeboard results in high weather helm? This means the wind does what it pleases to the boat. Even an 8 knot wind is hard to troll into because the bow needs to be perfectly pointed to windward. And so, to fight this, speed is needed. Eventually, only downwind trolling is possible.
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rick berrey
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Re: FS18 OFFSHORE

Post by rick berrey »

If you are going to scale you scale length / width , or length only . There are boats here that can go 5 miles out without a redesign and suited to your motor , just not 20' unless you settle on displacement speed . If you look at the GF18 you will find 25 hp / weight 475 / beam 7'1" , look at the GF16 and you find 15hp / weight 165 / beam 5'2 . The 5'2 beam is close to what you want , if you scale in length only you are at about 17'6" around the same length as the GF18 only a narrower beam . Tom could run the numbers but I would bet your 20hp would push a GF16+10% , and I would have no problem taking that boat out 5 miles , might be a wet ride .

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Re: FS18 OFFSHORE

Post by OneWayTraffic »

fallguy1000 wrote: Mon Oct 10, 2022 5:34 pm You are getting some bad advice.

The designer needs to coin in.

You do not use a 20hp engine and then add a lot of freeboard and mass down low to offset. This is design spiraling out of control.

Build the Panga 20. It is the right boat for the engine constraints you propose.

The FS18 with higher bulwarks is too much boat for the 20hp engine..and higher bulwarks is not something wise as it raises the VCG of the boat. And adding mass down low makes it harder to plane and pos buoyant? Probably not...

One of the guys mentions weather helm. Do you realize higher freeboard results in high weather helm? This means the wind does what it pleases to the boat. Even an 8 knot wind is hard to troll into because the bow needs to be perfectly pointed to windward. And so, to fight this, speed is needed. Eventually, only downwind trolling is possible.
Agree with most of this, especially the added freeboard. I’d definitely like to run that by the designer.

But the Pg20 would need to be built lighter for any kind of performance with a 20hp and the designer once stated that building it too light would lead to stability issues. I could be wrong and if even 15mph was doable with a pg20 then that would be my choice. It is very heavily built compared to similar sized boats. 13mm ply instead of 9mm, 9mm instead of 6mm.

The OP seems married to a 20hp, given that constraint what is the best boat to build for it?

If it were me looking to build the most able planing boat for a 20hp I’d go for the FS17 possibly scaled down and simple , the OB15 or the PG20 in that order. Unless the PG20 can go at a semiplaning speed with a 20, or could be safely scaled down to fit the 20hp. That would change things.

I’ve taken a 11ft dinghy further offshore than he plans to go. That had a 20hp as well. This was on the West coast of NZ with thousands of kilometres of fetch from Australia. I picked my days, the boat was unsinkable, with three times it’s weight in foam buoyancy and I learned how to handle it . If he picks his days with even a FS18, builds it right, puts buoyancy bags in the cockpit, wears a lift jacket and kill switch I see no reason why an FS18 will kill him, but it would never be the boat I’d choose first.

GF16s have been out that far as well. That’s no bigger than an FS18.

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Re: FS18 OFFSHORE

Post by pedroe »

fallguy1000 wrote: Mon Oct 10, 2022 5:34 pm
The designer needs to coin in.
That would be great.

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