Zodiac Splitting transom at engine bolts - advise needed please

mhb100 · 25 June 2007, 09:28

Guys

Theres some minor splitting near my top engine bolts on the transom of my Zodiac 550. I think (but am not 100% sure) that they first appeared (or got worse such that you could see it) after i had the engine bolts checked for torque when i was getting an engine bolt type lock fitted, just after purchasing

I also know the previous owner had an engine swap at some time, and we think the prop is most probably wrong as its top end is c5000 and 30knts max. The model is 1999, but has has less than 100 uses in that time.Its also always been stored on a trailer.

The cracks have been there for sometime now and are not getting any worse in any way and ive recently given it a few hard times and over several c50m day routes - so im happy its not getting worse.

The splits seem to go from the bolts and spread outwards about 6" max but theres virtually no splitting (less then an inch) the other way ie towards the centre of the engine.

Yesterday I took a grinder to the splits in the gel coat and basically these splits are actually where the back of the transom (the meety part) joins the front part of the transom, theres a very clear line where the 2 join which is exactly on the split. I have ground in deep to check for moisture and all is dry, there is no sign of any exposed marine ply, only fibreglass which is 'clean' - but it seems it was made as a box section as when you peer in the cracks you can see a hollow gap of about 1cm depth between the front and back. I'm assuming this is not the case where the bolts actually are, but of course I cannot see, and i dont want to cut good surfaces at this time.

There is also no form of any sealer on the inner edge of the join, so you have the rear meety transom (about 5cm thick) which thins to about 1.5cm at the lip joining the top section which is about 5mm thick material . The edges just seem to rest together and not actually come into any proper join, other than the gel coat - so no wonder the gel coat has split as I'm sure that vibration alone would have caused this overtime.

the first 2 picture were original and the last 2 pictures once I had ground and chiselled out any loose stuff.

Has anyone come across this before?

How best do i fix this?

I want to also check the bolt torques my self - any idea what they should be?

Cheers
Mark

jonmitch · 25 June 2007, 14:57

I am no expert, but my pal, a marine engineer who is, says that the engine bolts are placed far to high in the transom at its weakest point. He has suggested the engine is removed totally, the transom repaired and the engine resited in a more appropriate position.

What does everyone else think?

vince · 25 June 2007, 15:11

Totally agree, there is too much pressure on the 'lip' of the transom. The curved 'c' shape on the engine mounting plate, just above the bolt holes, is where the transom lip should sit in. This gives you enough up and down adjustment for engine height etc. At the moment, its way too high, and the lip is just cracking along the edge. The engine plate should sit flat on the transom.

Hightower · 25 June 2007, 15:18

Yes the bolts are close to the top of the transom, but only because the transom is too low in the first place.

The outboard can only be positioned in one of a small number of heights and performance and operational demands will dictate this. I take it your's is correctly positioned?

The Upshot of this is that the outboard probably cannot be relocated due to the above statement.

Yes, I have seen this before and I don't think it is a very serious short term problem and is caused by one of two things. 1...it's a manufacturing problem where the glass matt doesn't go right around the bend and the flex in the outboard and transom have expoited this weakness and split right along. 2...The transom is flexing too much and the result is this damage.

I doubt its problem number 2, unless there are other signs, such as cracks between the deck and transom or bottom of transom and the bottom of the hull. I would however do a repair ASAP as any water getting down the crack will soak into the wood core and cause problems later.

The correct way I would suggest removal of the Outboard and either strip back the surrounding fibreglass and re-glass the area or what I would do is to increase transom height and do the re-glassing.

Tims Osprey · 25 June 2007, 15:25

yep the engine has been fitted wrong and is way to high, the top off the engine mounting should sit nicely on or near the top of the transom and as the pictures show is mounted way to high, or as explained by hightower the transom is too low, this i think also explains your poor engine performance. The person or people that fitted the engine clearly did not have a clue, you will have to have the engine removed and have the transom repaired, i hope it's not too badly damaged, i would suggest having a stainless steel all round transom plate made up after any other repairs to ad strength, especially with that big Honda lump on the back.

Hightower · 25 June 2007, 15:29

Quote:

Originally Posted by Tims Osprey

yep the engine has been fitted wrong and is way to high, the top off the engine mounting should sit nicely on or near the top of the transom and as the pictures show is mounted way to high, this i think also explains your poor engine performance.

How do you know the outboards too high?

Sixy_the_red · 25 June 2007, 15:39

The engine is set correctly for the prop / anti-cav plate height (I saw the boat yesterday afternoon).

The only remedy in that case would be to get a shorter shaft engine, but I don't know what shaft length mhb100 currently has.

(BTW I'm Matt's g/f incase you were wondering mhb100!)

Hightower · 25 June 2007, 15:43

Quote:

Originally Posted by Sixy_the_red

The engine is set correctly for the prop / anti-cav plate height (I saw the boat yesterday afternoon).

The only remedy in that case would be to get a shorter shaft engine, but I don't know what shaft length mhb100 currently has.

(BTW I'm Matt's g/f incase you were wondering mhb100!)

Thant's what I thought might be the case.

One of three option then:

1. Keep the transom the same height and repair and reinforce the problem

2. Build up the transom height and make good.

3. Put a transom plate on either with or without the transom height being increased.

Tims Osprey · 25 June 2007, 16:06

The engine clearly is sitting on the transom way too high, i did not state that the engine was set at the wrong operational height, however after reading his previous post about poor engine performance this could be a possibility.

Endeavour · 25 June 2007, 16:33

As the Transom length for the honda is 537mm. It seems to me like the Engine is mounted fine.

Tims Osprey · 25 June 2007, 17:02

mhb100, do you get any prop ventilation or loss of power, especially when turning the boat at speed?

nikster · 25 June 2007, 17:20

being as it lives on a trailer - one of 3 options
1. disconnect engine and all cables etc and full repair or
2. undo bolts pull engine away from transom slide stainless plate in and rebolt on till end of season before performing 1 or
3. drill 3rd set of transom bolts into spare holes so that 6 bolts are holding it on till end of season - then perform option 1.

you should be crystal clear tho that being as you have now cut away you need to complete a temp glass repair otherwise as soon as water is in there - you will need to cut transom away completely and start again.....

Tims Osprey · 25 June 2007, 17:32

Is it just me but on looking at your pictures again there does not appear to be any engine mount bolts in the lower section of the engine mount?

top left hand picture i think shows this? probably wrong though just checking?

mhb100 · 25 June 2007, 18:24

Quote:

Originally Posted by Tims Osprey

mhb100, do you get any prop ventilation or loss of power, especially when turning the boat at speed?

Yes, Tim i do lots. I usually have to trim down if i intend to make a quick turn, its *iss poor. It does drive really well normally and i dont get any strange vibrations when i accelerate upto its max of 30knts its really smooth

Why what are you thinking mate?

mhb100 · 25 June 2007, 18:31

Quote:

Originally Posted by Tims Osprey

Is it just me but on looking at your pictures again there does not appear to be any engine mount bolts in the lower section of the engine mount?

top left hand picture i think shows this? probably wrong though just checking?

Tim heres a better picture - there are 2 bolts at the top and 2 at the bottom and i've done some checking on the history....

The original owner purchased from brand new in April 1999. The engine was 6 months old with 20hrs. As it has been serviced every year i have the honda history and it is a long shaft which is correct according to Zodiac. A laser 20 was fitted at that time - which might not be correct; too large?.The supplier was Outboard Services Lostwithiel Cornwall; who I'm assuming do what there doing so its not a novice DIY job. The engines alsways been in that position.

We purchased direct from the first owner (friend of a distant friend) who was not mechancial and left it to the engineers to look after so its not been messed with. Services have been done by the original suppliers and also some from a company called Pacer Marine Farnham several times.The engine does not appear to have been moved or altered in any way since fitment.

The bottomline is that this honda lumps been on their for the life of the boat. I have attached another photo now to show the whole engine - so hopefully someone else can confirm the heights looks right?

In which case its got to be down to poor construction?

Mark

Tims Osprey · 25 June 2007, 18:41

Quote:

Originally Posted by mhb100

Yes, Tim i do lots. I usually have to trim down if i intend to make a quick turn, its *iss poor. It does drive really well normally and i dont get any strange vibrations when i accelerate upto its max of 30knts its really smooth

Why what are you thinking mate?

excessive prop ventilation and loss of power usually means that the engine has been installed to high on the transom which i thought was the case, can't be 100% sure though without seeing it and taking some measurements, so get somebody else to look at it and see what they think? if i lived any closer i would come along myself to check it out, what is the measurement from the top of the transom to the hull from the middle?

Tims Osprey · 25 June 2007, 18:53

Trim the engine right down and measure the height of the cavitation plate to the bottom of the hull, is it level, just above or just under the hull?

yoyo · 25 June 2007, 18:54

Hi MHB 100,

Is the packing piece that is shown in your pictures the correct thickness? If it is slightly thinner than that "lip" it would put a large load in the area when the bolts are tightend, this could possibly cause the spliting. IMHO.

mhb100 · 25 June 2007, 19:09

Quote:

Originally Posted by yoyo

Hi MHB 100,

Is the packing piece that is shown in your pictures the correct thickness? If it is slightly thinner than that "lip" it would put a large load in the area when the bolts are tightend, this could possibly cause the spliting. IMHO.

Hi Yoyo

Just been and checked, Its not that thick but there is a gap about 3mm between the lip and engine bracket so its not touching or being compressed by the bolts at the moment

Mark

Tims Osprey · 25 June 2007, 19:12

It might be the prop though causing the ventilation, remember from a previous thread.