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motor not resting on transom?
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croakz



Joined: 21 Sep 2020
Posts: 104
City/Region: Seattle
State or Province: WA
C-Dory Year: 1997
C-Dory Model: 22 Angler
Vessel Name: Jolly Blue
Photos: Jolly Blue
PostPosted: Mon Aug 09, 2021 6:10 pm    Post subject: motor not resting on transom? Reply with quote

Hi,

I was able to get re-powered with a Honda BF100, so far pretty happy with it.

I did have a question about the motor placement, as it's not resting on the transom. It's being held on by 4 bolts. Is this normal? Thanks.

- tom

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colbysmith



Joined: 02 Oct 2011
Posts: 4523
City/Region: Madison
State or Province: WI
C-Dory Year: 2009
C-Dory Model: 25 Cruiser
Vessel Name: C-Traveler
Photos: C-Traveler and Midnight-Flyer
PostPosted: Mon Aug 09, 2021 7:13 pm    Post subject: Reply with quote

Both my 22 and 25 were the same way. What's important is to have the motor at the right height on the transom.
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T.R. Bauer



Joined: 17 Nov 2007
Posts: 1726
City/Region: Wasilla
State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Mon Aug 09, 2021 7:47 pm    Post subject: Reply with quote

Yes it is normal.
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DayBreak



Joined: 16 Jul 2017
Posts: 838
City/Region: Monmouth, Or.
State or Province: OR
C-Dory Year: 2018
C-Dory Model: 23 Venture
Vessel Name: DayBreak
Photos: DayBreak
PostPosted: Mon Aug 09, 2021 8:00 pm    Post subject: Reply with quote

T.R. Bauer wrote:
Yes it is normal.


Agreed. This may be an indication that consideration was given by the installer for proper height to attain best speed and fuel economy on your given boat.

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Gary F
DayBreak, 23 Venture, 2018 - present
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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Mon Aug 09, 2021 9:05 pm    Post subject: Reply with quote

Normal, but best practices is to put a compression plate between each set of bolts (Top and Bottom) to spread out the load. Think of the area of a plate 3" x 18" vs the typical fender washer or the amount of structure on the outside of the transom motor mount.
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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL
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ssobol



Joined: 27 Oct 2012
Posts: 3361
City/Region: SW Michigan
State or Province: MI
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: SoBELLE
Photos: SoBelle
PostPosted: Mon Aug 09, 2021 10:57 pm    Post subject: Reply with quote

My 22 is that way too. Sits about an inch above the transom.
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croakz



Joined: 21 Sep 2020
Posts: 104
City/Region: Seattle
State or Province: WA
C-Dory Year: 1997
C-Dory Model: 22 Angler
Vessel Name: Jolly Blue
Photos: Jolly Blue
PostPosted: Tue Aug 10, 2021 12:08 am    Post subject: Reply with quote

Thanks all!
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san juanderer



Joined: 12 Aug 2014
Posts: 234
City/Region: Stanwood
State or Province: WA
C-Dory Year: 1990
C-Dory Model: 22 Angler
PostPosted: Tue Aug 10, 2021 2:17 am    Post subject: comment from a very wise aluminum boat fabricator ( not me ) Reply with quote

As everyone has said " it is normal " !

From the wise guy;

Sitting static, there is very little structural pulling on the fender washers.
Trailering down some bumpy road or down some logging road out in the far north, then there can be some pulling on the transom.
But underway, that motor is pushing on your transom very hard. The fender washers are not part of the equation of your worry, nor the gap.
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T.R. Bauer



Joined: 17 Nov 2007
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City/Region: Wasilla
State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Tue Aug 10, 2021 4:56 pm    Post subject: Reply with quote

Not that any of it matters in one bit in real application, but doesn't the outboard both push and pull from a vertical axis at the same time while underway?
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ssobol



Joined: 27 Oct 2012
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State or Province: MI
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
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Photos: SoBelle
PostPosted: Tue Aug 10, 2021 7:03 pm    Post subject: Reply with quote

T.R. Bauer wrote:
Not that any of it matters in one bit in real application, but doesn't the outboard both push and pull from a vertical axis at the same time while underway?


Most of the force an outboard generates when pushing a boat is a torque that is basically trying to peel the transom off the back of the boat. The vertical load on the transom from the weight of the engine is small in comparison.
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thataway



Joined: 02 Nov 2003
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C-Dory Year: 2007
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Photos: Thataway
PostPosted: Tue Aug 10, 2021 7:11 pm    Post subject: Re: comment from a very wise aluminum boat fabricator ( not Reply with quote

san juanderer wrote:
As everyone has said " it is normal " !

Sitting static, there is very little structural pulling on the fender washers.
Trailering down some bumpy road or down some logging road out in the far north, then there can be some pulling on the transom.
But underway, that motor is pushing on your transom very hard. The fender washers are not part of the equation of your worry, nor the gap.


Au, if only this were true. In reality there are multiple forces acting on the transom--including torque, downward, and lateral, as well as rearward pull.

Have you seen a transom fail with fender washers crushing into the laminate? I have.

Have you hand held a 25 hp outboard on an inflatable transom which failed? I have.

Have you seen a transom which failed in the center--below the outboard support, and pull ward when under way? I have.

The forces are complex. and the better support one has the better that transom will fair.

I hope that you are not advocating that only fender washers are the best way of mounting an outboard on a transom.
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T.R. Bauer



Joined: 17 Nov 2007
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State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Tue Aug 10, 2021 9:45 pm    Post subject: Reply with quote

I agree with Bob and others - it is complex. The outboard acts as a lever while the boat is propelled forward and the top part of the transom is pulled the other way in order for this to happen. There is also a left to right loading on the transom while underway.....anyways not exactly simple - especially when you toss in sea conditions. The point is, you better have a solid transom:-)
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san juanderer



Joined: 12 Aug 2014
Posts: 234
City/Region: Stanwood
State or Province: WA
C-Dory Year: 1990
C-Dory Model: 22 Angler
PostPosted: Wed Aug 11, 2021 1:59 am    Post subject: Reply with quote

This "wise guy " boat yard is full of Alaska fishing boats shipped by land down here to WA State for all kinds of construction and modifications. He used to build fiberglass boats then got into the aluminum boat building business.

He has built two outboard pods for me over the years, I had all kinds of questions about the structural aspects, and the 300 hp outboard hanging 30 inches setback from the transom. He assured me with his years of experience.

I will trust the boat builders comments, not the Dr. in the house.

Sorry for being blunt, but the internet is full of " experts ".

Sorry Dr. Bob
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T.R. Bauer



Joined: 17 Nov 2007
Posts: 1726
City/Region: Wasilla
State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Wed Aug 11, 2021 2:45 am    Post subject: Reply with quote

Perhaps we should leave it as a solid transom is very important.....arguing over the forces at play will not bear much fruit.
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thataway



Joined: 02 Nov 2003
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C-Dory Model: 25 Cruiser
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Photos: Thataway
PostPosted: Wed Aug 11, 2021 10:44 am    Post subject: Reply with quote

Despite your "expert" I stand by what I said. It is prudent to put a full bar on the inside of the hull rather than fender washers. Especially on the C Dory. We see lots of "Manufactures" consistently make mistakes in the boat building process. Often those who build or modify boats don't have the experience of those who look at the failures. or run boats for many years.

For example best practice would be to put some structural component inside of the transom where the bolts go thru, such as an epoxy plug to seal the core. How many boat builders do this? Hopefully the fellow who made the "pods" for you used best practices. (I have seen some pretty innovative melding of fiberglass boats with aluminum aft sections, as the transom book down in the AK freeze thaw cycles).

Hopefully your "expert" used best practices when he attached a pod to a transom--and that would include a backing plate, and sealing any wood or foam in the transom, especially in boats used in AK.

How about thru hulls in the bottom of the boat? A responsible builder will but a solid glass plate int he way of cleats, thru hulls under the water etc. Why do almost all of the 25's have core issues around the cockpit hatches and steps? It costs more to put a solid structure or seal the core. Same with fasteners into the bottom of the hull. I have been asked to see a number of issues in hulls from migration of water from these, where there was breakdown of the core/laminate.

Actually C Dory does it pretty well. You would not believe how many manufactures handle the hull to deck joint. It is solidly glassed over. Many just put some bedding compound and a U/U channel. Others just pop rivets with bedding compound. Picture the surprise of an offshore sailer, when the entire deck molding starts to come apart hundreds of miles from land!

Ask a couple of these folks who had to recore almost the entire bottom of the boat because where only a few screws had allowed water intrusion?

In fact the fiberglass interior is stronger and better because there are no zinc plated "L" brackets with multiple core penetrations. (They could have been put in with tabs of glass, instead of the cheaper and more easily done way it is done.)

How leaks between the area under the cockpit, which were not adequate tabbed in and the aft bulkhead not sealed, where core material eventually developed rot?.

Yes I worked as an MD. That has little to do with my boating experience. I first worked with fiberglass boats in 1952. Since then I have been interested in the negative structural issues with fiberglass boats. However I have been interested in osmotic issues since college and that lead to my being one of the first nephrologists. The kidney is an osmotic machine...Thus the interest in laminates and osmotic issues.

I saw delimitation in some of the 1960's boats, and then followed osmotic blistering as the problem with laminates appeared. I looked at over 100 boats in Europe which had bad blistering. I had inside information on issues with both Cal Yachts, and Columbia/Coronado Yachts, as to problems. More recently in the mid 2005 era had access to over 20 boats to cut up and analyze cores in both hulls and decks as I helped a friend modify NDT instruments to give a good tool for boat builders and surveyors to actually give a true picture of water intrusion and delimitation. Guess what? The marine surveyors didn't want to pay $2,000 and take a few days to learn how to use the instruments. Only a few high end builders were interested. So we all remain in the dark ages--the NDT for boat laminates never came to fruition. It is pure economics and perhaps some laziness.

My only dog in the fight, is that we as owners and builders should follow best practices rather than save a buck or two.
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