crack in transom's vicinity

[harrold101]

Recently we have fitted a new outboard (150hp etec) to a 1970's 18ft cruise craft, which 6 years ago had a 135hp 1970s evinrude fitted.

The newly done up boat (paint job and all) has only been out twice and during the second trip we noticed a crack developing on the drain hole of the splash pit, there is also a few stress cracks on the pit, though were there before the outboard was fitted.

after further investigation i also found a tiny crack on the transom inside of the boat, although it looks like an old crack.. there are no other visible signs of cracking or splits.

wondering if anyone else has had similar problems, know a solution cheaper than having a complete rebuild? Was thinking a checkered stainless plate?

cheers

[Benzeenees]

150 hp seems a bit big for an 18 ft boat. Maybe that's part of the problem?

[John C]

I would get it looked at professionally the new motor wouldn't be heavier than the older motor even though its got bigger horse power and 150hp should be fine my 18ft boat is rated to a 150hp.

[Day's Fishin]

Mate sorry to say but you will have to replace the transom. Nothing to do with the HP (in my opinion) just age and stress.

Regards Jeff

[Testlab]

That crack around the drain would be enough to let water in and weaken or rot the substrate, so it has to be dealt with. The stress cracks may have been developing for a while but the action of changing the engine over may have exacerbated any weakness that's been building for some time.

You can drill a few holes in the transom and check for water ingress and rotted plywood. If its clean and in good shape fill them with epoxy. When the engine was installed were the bolt holes sealed properly?

You may need to check if the transom is moving excessively. Years ago I was shown to do this by sticking a long, narrow piece of scrap ply to the top of the transom, perpendicular to it (so it is aligned fore and aft), nestled against the engine brackets and secured with a dab of silicon. The ply is long enough to project over the well or some other reference point in the boat. Make a mark on the ply where it cross the datum point, say the forward edge of the well.

Raise and lower the engine or go for a run and make marks on the ply showing the furthest extent of flex in the transom. I don't know what is the maximum amount of flex before saying its good or bad, but this will give you some solid data to ask an expert who is familiar with that type of boat.

[Guest Aussie007]

i think it would be the power of the new engine vs the old worn out 70's model engine the power difference from old to new is a fair amount from my observations plus u went up to 150hp i also think the 135hp engine back in the 70's was rated at the flywheel not the prop so it would be less than 135hp

ive owned only one large boat it had a 140hp on it plenty of get up and go was 18.5ft i'd say a modern 90 would be sufficient on a 18ft general fishing boat

[harrold101]

i think it would be the power of the new engine vs the old worn out 70's model engine the power difference from old to new is a fair amount from my observations plus u went up to 150hp i also think the 135hp engine back in the 70's was rated at the flywheel not the prop so it would be less than 135hp

ive owned only one large boat it had a 140hp on it plenty of get up and go was 18.5ft i'd say a modern 90 would be sufficient on a 18ft general fishing boat

The old engine was 115hp at the prop, and got to 25 knots unloaded, since that the boat has had its floor thickness doubled and other hardware added.. although in saying that with the Etec now, we had it up to 40knots in still waters with 3 people, minimal gear.

I have seen some flex while giving it a run, wasn't a large amount and only saw it going over swell at speed, though any is not good.

Is there any other way of supporting or fixing the weakness rather than a rebuild, just the cost that has already spent on the boat steers me away from that option

cheers for the replies

[pjbink]

It's hard to tell whether the cracks are from a serious fault or not as it is not unusual for gel coat to crack and craze. You can check for flex by pushing up and down on the motor when it is in the tilted up position. Obviously there should be no movement in a healthy transom. You can check for rot by tapping around the trasom with your knuckles or a small hammer covered in cloth. Rotten sections will have a dull sound.

[Guest Aussie007]

samy u were given the best reply on the other sydney forum by Juggs who is a member here i believe

what is the hull rated too ?

has the transom been repaired?

1970 135 is about 105 hp at the prop and 123kg or so

the etec is 150hp at the prop and some more and 196kg

so you've added 45 + hp and 70kg to the transom of a 40 year old boat, id say that's what went wrong

some of these old boats just cant cope with the addition of newer motors, the old johnos punched really hard for their weight

newer engines are bloated heavyweights in comparison

ive seen transoms caved in from the above scenario, you' will have to take it to a fiberglasser and get the transom repaired and beefed up

your E-Tec is to big for the boat you've done damage to the transom and u will need it repaired