FS155 (FS17 scaled to 90%) Completed

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michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

Quick update - I have 3.5 hours on the motor, love it thus far. Took it out in fernandina beach on Sunday on the inside for break-in. Managed to scrape the new off on an oyster bed - I miss the sandy bottoms and clear water where I'm from :oops:
I had the 12 pitch 3 blade on until I scraped the oysters, which happened before I was far enough along in break-in to plane. I decided to swap on the 13 pitch 4-blade then (no major damage, but a few notches to sand out). That 13 pitch is going to be a great economy prop. I only got brief periods of 5/8 throttle in during the last few minutes (6.5 hours of break-in to go) but it was cooking along around 29 at about 5300 rpm's. It allowed me to trim the bow up a good bit without blowing out. It should be good for long flat water runs. When freediving alone, I'm often really lightly loaded, and I like the idea of being able to run a long way at almost 30 and keep it well below the limit. I think the 12 pitch it came with will probably be a good "all-around" prop (already filed it smooth), and I have an 11 pitch 4 blade on the way, for the rare times when I have a bunch of dive gear, couple people, etc. I'll test both of those this weekend. I'm spending 5 days of vacation in the panhandle at the end of next week, so I'll be able to give a report of its performance on water I'm intimately familiar with.

Regarding trim, weight, and transom height: I left the scupper valves off to check weight. It's still fully self bailing with just me and my dog aboard, although a (tiny) bit runs in when you stand on one side. None at all if you're moving at even idle speed. This is with battery, gas, and cooler 24-30" from transom. I'll be moving the group 24 battery about 5 feet forward soon. For a 15.5' boat with a 165 pound motor on the transom, that's not bad :-). Transom height appears good, although I haven't pushed hard on turns yet. I can trim up without blowout (at least on the 4-blade) and no hint of water flow issues.

One side note: although I love my electric start, the new DF30A is also ridiculously easy to pull-start. The last pull start I had was a 15hp tohatsu, and I swear this feels like it takes half the force, and it starts on a half pull. I mention this because the 25hp version has a bare-bones tiller option that only weighs 137 pounds. When you account for being able to delete the starting battery, it puts you in old-school 2-stroke territory. It's a good option for several of Jacques open designs like the gf16, where a 25 hp is nice, but you don't necessarily want the average 4 stroke plus battery on the transom of a boat that light.

michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

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ignore the construction mess.

michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

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more work to go, but getting there...

michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

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michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

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It has approval from the most important person in the house...

TomW1
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Re: FS155 (FS17 scaled to 90%) Completed

Post by TomW1 »

Michael the boat looks good. Next week end when you get her broken in you should have top rpm's above 5800 for both your props. If not go down an inch or two in pitch, one inch increases 200-250 rpm's.

Regards, Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

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Above is at about 22mph, dogs and wife all happy :-)

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Some pic's of the current setup. Plus my dog trying to get me to let her have fresh mackerel sashimi, as usual.

michael c
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Re: FS155 (FS17 scaled to 90%) Completed

Post by michael c »

Everything worked well. Still plenty to do, but I'm happy with it. BTW, for the baitwell lid/seat in front of console, I used a 40 lb magnet (stainless housing). Worked really well... plenty of holding power even trailering at 75mph, but looks slick because there's no latch.

I'm going to continue to play around with prop's. The boat itself just doesn't feel as good at 30mph compared to 25-27mph. That's likely because I faired smooth but didn't completely remove the slight hook from the buildup of layers of glass/tape at the bottom of the transom. I left it in because I originally though I'd be running an old 25hp forever. That leaves a very slight trim tab effect. I kind of like having it overall. It runs really well at lower planing speeds, with sweet spots at about 18mph in moderately rough water, 22mph in light chop, and 25mph in flat water with full load. No porpoising or issues at those speeds/conditions. Still feels great at 27mph. At about 29mph, it starts to feel like it's fighting too much when you trim up, resulting in a bit of porpoising. That said, it's a 15.5' boat meant do do a bit of everything, and I almost never use it in really sheltered areas. Most places I use it, anything much above 25mph is wasted on a boat this size. There's usually enough chop that you trade your kidneys/back for a couple of mph.

Overall, the taller transom makes it feel more seaworthy, as does the center console. Easy to manage, even though I took it out several days in small craft advisories.

Prop thoughts: The 11-pitch 4-blade is great when loaded and running with some swell. It sticks even running down swell at barely planing speed and/or trimmed up, and has lots of power. Although with a 29mph max speed (full throttle) it gets the powerband where it's "supposed" to be, I don't like it as an all-around prop. The rev's just feel excessive at 25mph (where the hull feels best) with 2 people, when even a 13 pitch gets there easily and holds it at 4700 rpm's.

The 12 pitch it came with works well in flat water, but it lets loose a lot quicker offshore with a lot of trim and running downwind. Rev's frankly still feel excessive, although I haven't tried it with a heavy load. Probably a good all-around prop, but I think the 4-blades complement the boat better. They just seem to hook up quicker, and are noticeably better in swell. I may go with a 4-blade 12-pitch as my general-purpose prop.

The 13 pitch feels the best in nice conditions. It doesn't really struggle to get the boat on plane, but gives much more reasonable rpm's at the most comfortable cruising speeds (20-26mph). I've always heard the advice about trying to get the top speed paired with nearly max rpm's, but I'm not sure it applies here. The limiting factor isn't power, but rather the fact that the hull feels better at mid-to-upper 20's than 30mph. In other words, the motor doesn't feel bogged down or underpowered at low speeds, and I don't need higher rpm's to push a load (most times). I don't see any benefit in adding mechanical strain from running higher cruise RPM's. I think I'll stick with a 12 or 13 pitch, and swap out for the 11 pitch when I'm going out for multiple-tank dive trips with a couple buddies. Slip on both 4-blades at 4500 rpm and up was generally around .08, so can't complain there.

Overall, I think the boat/motor combination is great. Any more power would be wasted, any more weight on the transom would cause trim issues. I think it would be a good motor even on the full-size fs17 with a small console, and I'm extremely glad I didn't go with a 40hp. As it stands, the boat has enough bouyancy to be left safely at dock indefinitely without any scupper plugs, and the 30hp has enough power to run it above 25mph with a couple of people on board.

jorgepease
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Re: FS155 (FS17 scaled to 90%) Completed

Post by jorgepease »

Nice boat ) My neighbors dog looks just as intently at every fish we bring on board!

Maybe I understood wrong but the idea behind being able to achieve max rpms is not that you eliminate strain on the motor at all rpm ranges. If you can't get her into the upper rpm range at WOT then your adding stress at whatever rpm you run.

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Re: FS155 (FS17 scaled to 90%) Completed

Post by remedy32 »

Overall, I think the boat/motor combination is great. Any more power would be wasted, any more weight on the transom would cause trim issues. I think it would be a good motor even on the full-size fs17 with a small console, and I'm extremely glad I didn't go with a 40hp.
Nice build and great comments in your last 2 posts! After 5 seasons with the FS17 I agree on all the points you've hit. The attraction of more power seems to cloud peoples thinking sometimes. This boat whether 15.5 or 17 feet LOA is most comfortable at speeds of 20-25 and not too much more. Because it's light it planes at relatively low speeds in the 12-18 mph range with minimal pitch change. Comfort goes way down if you insist on running fast in choppy water, why bother? Would agree that a light and simple tiller skiff would probably work real well with your 25-30 hp power choice. The C/C model with raised sheer is very happy with my aging Yamaha 40. Enjoy the boat!

Bill

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