outboard mounting hight problem

beerbelly · 09 February 2020, 07:11

hi folks I have just taken delivery of a new Humber destroyer 5.5 and the first problem while rigging it has arisen .my outboard turns out to be a 25inch leg and my transom is only 21.5 inch

I know but here I am .I have hung it on the lowest mounting holes and the vent plate is approx. 5mm below the keel line and the outboard is on its highest setting .will this be ok or should I buy a jack plate such as

https://www.ebay.co.uk/itm/CMC-Stati...EAAOSwK-1dH3el

I don't want to buy another outboard as quite frankly I cant afford one and this mercury f100 has less than 50 hours and runs sweet as ( it looks like it was mounted quite low on the valiant I took it off and was ok if a little slow at 35knts . thanks

beerbelly · 09 February 2020, 07:14

a pic of the outboard hight. sorry its on its side cant figure out how to rotate it

mikehhogg · 09 February 2020, 09:27

ideally the plate should be level with the bottom profile of the boat. I cant see 5mm making a huge difference to performance especially if you can still trim it.
There is only one way to find out though and that's a sea trial.

Ribtecer · 09 February 2020, 09:54

^^^ pretty much what I was going to say, just try it - although not today I might suggest.

If it works ok I would make a neat plug to fill the gap and make it look intended to the untrained eye.

Best of luck with it.

beamishken · 09 February 2020, 10:03

Idealy you would have the av plate slightly above the keel line for least drag and best performance. I usually start fitting about 1"up from level and adjust from there after sea trail, rarely do you need to go down. Occasionally you can go up and gain a knot or so dependingin the boat. That said if yours is a little deep and you lose a knot or two without any unusual handling tendencies then probably an acceptable compromise.
As others have said take it out and try it see how it goes

beerbelly · 09 February 2020, 10:25

thanks folks yes I am going to try it before deciding what to do .and no it wont be today still a few jobs to do yet

Ribtecer · 09 February 2020, 11:00

With a 100hp on a 5.5, I don't think a loss of a knot will be noticeable.

You'll be to busy trying to hang on.

beerbelly · 09 February 2020, 11:16

thanks I was thinking to get the jack plate even if its just to add some reinforcement to the part of the saddle unsupported above the transom

Ribtecer · 09 February 2020, 11:24

Quote:

Originally Posted by beerbelly

thanks I was thinking to get the jack plate even if its just to add some reinforcement to the part of the saddle unsupported above the transom

Take it out and give it a gentle test, if all is good that could be a worthwhile avenue to explore to help support for rougher harder conditions.

jeffstevens763@g · 09 February 2020, 11:36

not as you but my new sib is the same 10 mm below keel not tested yet but i'm not expecting any significant difference. for you the jack plate will sort it in any case BB

Locozodiac · 09 February 2020, 14:42

Post a picture of the lower leg shot sideways....

Happy Boating

Phil M · 09 February 2020, 16:48

My anti cav plate on my 5.8 is about 20mm above the keel line and I still think it could go a little higher. I think you'll get quite a lot of water shown up with it that low. I had the other problem as the 20" transom was nearer 22" so I can't go any lower.

Phil M

Last Tango · 09 February 2020, 20:33

As everyone has said......give it a try.
"If it ain't broke don't fix it"

tiverton_tom · 10 February 2020, 17:48

just remember if you have steering by cable/rod, you might need a new one, adding jackplate (been there, done that), ie. you might need a few more inches ... possibly not if you have hydraulic steering lines.

tiverton_tom · 10 February 2020, 17:54

this is from a Facebook post on topic of proper mounting height (options)

https://www.facebook.com/photo.php?f...type=3&theater

tiverton_tom · 10 February 2020, 18:05

this was original post:

https://www.facebook.com/groups/1310...20894034609777

Solgear · 12 February 2020, 17:15

I have taken a 2 transoms built for a short shaft and converted them into transoms for a long shaft. I used plywood glued together and then resin coated and cut out to fit perfectly on the transom with the same width. Then I plate both the front and the back with aluminum covering the entire transom and cutting holes for the scuppers. This aluminum is through bolted in 4 corners, plus through bolts on the piece that holds the floor down, plus through bolts on the motor and I have struts that bolt to the floor and attach to the transom with through bolts. Every hole gets resin or 100% silicone at the least. The transom is more rigid than it was to begin with and with the struts I'm able to transfer energy through the boat and not work the transom so hard. I run these boats down class V rapids on the Colorado River.

John Kennett · 12 February 2020, 21:18

Quote:

Originally Posted by Solgear

I run these boats down class V rapids on the Colorado River.

That sounds cool. Have you got any video?

beerbelly · 26 April 2020, 17:02

well I tried it. love the Humber a much more comfortable ride than the valiant was quite choppy with 30mph easterly's and a meter or so swell and it was comfortable around 20knt mark didn't go out far as we were filming some racing yachts but I am happy with the rib .unfortunately the outboard being low did make itself felt there was a lot of water splashing up around the transom and it felt flat we went into some flat water in the old Victoria dock and just couldn't get it over 32knts .so I have decided not to add the jack plates I have bought and risk my lovely shiny new outfit looking cobbled together I have bitten the bullet and put a deposit on a new 115 mariner. to be collected after the lockdown . oh all this testing was done before the travel restrictions

Locozodiac · 01 May 2020, 01:04

Had same exact issue, my fast responder 430 Rib was not an S or L height transom, had excessive water splashes at back transom when on plane while being powered with a 2 strokes L 18 HP motor. Didn't wanted to install a transom mount or an exterior jack plate to rise the motor and lower leg as well, just a cheap device that would stop the excessive water splash. In a moment of true enlightenment and deep thinking turned duplicating the original lower fin with an epoxy putty.

The fake fin was tested at several lower leg heights till the water splash was totally canceled out, then glued to the final lower leg's front resting position with an aersospace glue, Works as a charm..

Happy Boating