FS14 Build - Pics, etc.

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Jeff
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Re: FS14 Build - Pics, etc.

Post by Jeff »

Lets wait and get a response from Jacques. Jeff

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Re: FS14 Build - Pics, etc.

Post by jacquesmm »

See this:
https://boatbuildercentral.com/support- ... ansoms.pdf
In that tutorial, I explain that for planing, the cavitation plate should be flush with the bottom but for displacement speeds, it should be a couple of inches lower.
That is not my opinion or my preference, it is a well accepted practice.
The industry standards (ABYC and ISO) are 15, 20 and 25".

I did not know that Honda made 22" shafts. Do you measure as in my tutorial?
If that's the case, maybe they have a special model for displacement hulls.
I know those exist in Tohatsu and Suzuki but they are rare and usually special order.
Also, they have larger props and a different reduction gear.

The transom can take the bolts with large washers but a Al backing plate never hurts.

Talk to your Honda dealer.
I checked the Honda web site and it looks like the BF20 is always 15 or 20".
Jacques Mertens - Designer
http://boatbuildercentral.com

finalfront
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Re: FS14 Build - Pics, etc.

Post by finalfront »

Thanks for chiming in Jacques. (I did look at tutorial)
Honda bf20d manual I have for my model (1600000 models) does say it's a 22.2 inch shaft for long shaft in installation section. Honda dealer (&boat maker) confirms the 22" & says different engines do vary & it's fine with this engine to have anti-ventilation plate below bottom (manual says 0 to 2 inches below ok). He said he'd try it & only raise if an issue.. After more discussion we agreed raising it an inch (thus only 1"below hull) would be good compromise.
Thus top of bracket will be 1" above top of transom & engine solely supported by bolts.
Question: should all 4 bolts be in the thicker clamping board section of transom? Right now, the two bottom bolts are in section just below clamping board section. (also keep in mind I did two pieces of 3/8" ply for whole transom & two more at clamping section, so 3/4" below clamping board).
*I agree & was thinking of using alum sheet piece inside to distribute load along with large washers.
Hoping to get it done tomorrow...
Jacques, Any more advice is greatly appreciated.

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Re: FS14 Build - Pics, etc.

Post by finalfront »

Here's pic of manual page.
Screenshot_20200818-083527_Adobe Acrobat.jpg

jacquesmm
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Re: FS14 Build - Pics, etc.

Post by jacquesmm »

This is weird but Honda outboards 20 HP or less have longer shafts. Check the specs of a 50 or a BF25, the standard shaft is 20", not 22.
I know that's the case for some engines less than 10 HP but all other 15 and 20 I know are 20".

Anyway, for the bolts question: the bolts must be in the full thickness area.
For those lower bolts, use a backing plate, that means, epoxy glue layers of plywood below the existing clamping board to match the thickness of the clamp.
It is below the aft deck, not visible.
Jacques Mertens - Designer
http://boatbuildercentral.com

finalfront
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Re: FS14 Build - Pics, etc.

Post by finalfront »

jacquesmm wrote: Tue Aug 18, 2020 9:33 am This is weird but Honda outboards 20 HP or less have longer shafts. Check the specs of a 50 or a BF25, the standard shaft is 20", not 22.
I know that's the case for some engines less than 10 HP but all other 15 and 20 I know are 20".

Anyway, for the bolts question: the bolts must be in the full thickness area.
For those lower bolts, use a backing plate, that means, epoxy glue layers of plywood below the existing clamping board to match the thickness of the clamp.
It is below the aft deck, not visible.
I can squeeze all 4 bolts on existing clamping board now (bottom two will only be about 1/2" up from transition of clamping bd to bottom section). Or, as you say, I can just add about 3" of 3/4" ply board under clamping board & use holes I've already drilled. (likely with alum backing plate for all 4 bolts).
Which will be best.. Heavy engine and all?

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Re: FS14 Build - Pics, etc.

Post by VT_Jeff »

Boat looks great, finalfront! I have a very old copy of Wooden Boat in my "reading room" and it features the Simmons Sea Skiff, your boat has some similar features as that, which I like a lot.

Here's my .02 based on some info I found in this article: YMMV, literally in this case.

I'm going to let the lower unit hang a little low and not worry about it. Extrapolating the data shown below down to my expected speeds, the calculated loss is negligible. I may be searching for info with bias, admittedly. IMO, the vent plate is going to plane whether it's at the surface or 2" below, and I'm sure the reynolds numbers are not there for attached flow in either case. It's a plate, not a foil, so it's not going to recover any energy. The extra 2 inches of drag may cause me to burn an ideal 2.2 GPH at WOT instead of an ideal 2.0 GPH at WOT, but I'm not willing to start changing my transom for that savings at this point. My last boat was 11.5 GPH at WOT so I am already WAY ahead of the game.

Please take my analysis with a grain of salt, I know barely enough to be dangerous on most of these topics.

https://media.channelblade.com/boat_gra ... tricks.pdf
LowerUnit.JPG
There are only two seasons in Vermont: boating season, and boat-building season.

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finalfront
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Re: FS14 Build - Pics, etc.

Post by finalfront »

Thanks Jeff.
I'm going up 1" & thus 1" below. Good middle. Appreciate the article & thoughts.
Thanks Wes

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OlivierP
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Re: FS14 Build - Pics, etc.

Post by OlivierP »

When I built my GF14, I checked the specs of several engines 10-15hp, and as it happens, to my surprise most "long shafts" were 22" long instead of 20 : Honda, but also Yamaha and Tohatsu, if my memory is correct only Suzuki made real 20" shafts. Therefore I built my transom 22" high, because it's easier to shorten than to extend... I ended up buying a 9.9 Yam and it is perfectly flush with the bottom on the 22" transom.

Your FS looks fantastic, congratulations!
Built C17 (app.php/gallery/album/262), GF14, Devlin Bella 16. Sails a 30ft Biloup 89 sailboat.

finalfront
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Re: FS14 Build - Pics, etc.

Post by finalfront »

OlivierP wrote: Tue Aug 18, 2020 2:17 pm When I built my GF14, I checked the specs of several engines 10-15hp, and as it happens, to my surprise most "long shafts" were 22" long instead of 20 : Honda, but also Yamaha and Tohatsu, if my memory is correct only Suzuki made real 20" shafts. Therefore I built my transom 22" high, because it's easier to shorten than to extend... I ended up buying a 9.9 Yam and it is perfectly flush with the bottom on the 22" transom.

Your FS looks fantastic, congratulations!
Thanks, that's what my Honda dealer said that most are 21" or 22".. Live & learn.

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