Trim tabs and underwater exhausts

[Bertramdriver]

Because the exhaust comes out of the side of the boat not the transom.

Ok, but same principle applies
I too would hesitate to knock big holes through the bottom of my hull so I would go for an above waterline solution.
If you're competent with GRP why not make up an external fairing to redirect the flow down the aft section to the transom and angle the flow into the slip stream. A bit of a challenge on the stylistic side but an interesting project.
These fairings were very popular on Italian boats in the 80's and do appear to work.

 

[Elessar]

Ok, but same principle applies
I too would hesitate to knock big holes through the bottom of my hull so I would go for an above waterline solution.
If you're competent with GRP why not make up an external fairing to redirect the flow down the aft section to the transom and angle the flow into the slip stream. A bit of a challenge on the stylistic side but an interesting project.
These fairings were very popular on Italian boats in the 80's and do appear to work.

the later versions of my boat do exactly that. But they are vulnerable to damage.

The holes in the bottom of the boat really don't phase me. Seriously thinking about this.

Paul's point about the salty air my only concern.

 

[Elessar]

Exhaust outlet through hull means a very short run of pipe, it also eliminates the down angle problem from the riser or elbow as many boats require an "up" from the turbo before it can drop so not to allow sea water back in the turbo.

A direct drop is easy straight out into a silencer which on most boats I've worked on is moulded to the hull.

This set up always makes me question in my own head and there all "Ifs" but should the moulding delaminate away from the hull your going to let water in, I've seen a few boats having gel repairs in this area where over years a problem has started, mainly Azimuts so I'd check yours Rafiki, water stains and rust marks seem to appear.

The other downside is that you have sea water a lot nearer your turbo with salty air and no way of blocking it off unless you remove the exhaust elbow, this will corrode the turbo housing and vanes, which is the norm on most sterndrive installation...

Elessar you could fit different risers and then the dustbin silencers in the engine bay, or copy a sealine 42/5 installation where it drops straight out the bottom .

I need to look at a 42/5 never seen the engine bay of one.

If I put dustbin silencers in the back of my engine bay, any access to gearbox or port battery, or stern glands would be impossible. Even getting them in may not be possible there is very little room. If I did that I would have to have a clamp together fitting in the exhaust so they could be quickly removed. The slide on and clamp type of fitting is just too difficult to remove.

 

[Elessar]

Hmm, you can get 4" brass scoops. So not even GRP work required just drill a hole.

so if i go to a Y after the water injection, take a 4" hose straight out through the bottom of the boat and a 2" hose through an in line muffler (small hose = small muffler) through the existing exhaust outlets.

Would this work?

 

[Nigelpickin]

Finally after a lot of boats viewed we've found the model we want. Thanks to everyone for your help. We've decided on the Jeanneau Prestige 50s. We've found one in France and are off next week with a view to buying. I've noticed that the Prestige does not come with trim tabs as standard. I'd like to know your thoughts on this. Also the boats have underwater exhausts can anyone inform if there any advantages/disadvantages to this system, other than less noise and exhaust smell etc. finally the boat is offered on a French Jeanneau agents site and states that the boat will be freshly anti fouled and engines serviced prior to handover. The boat comes with a 2 year eyb. Warranty has anyone had any experience of dealing with issues with these warranties, and is it usual practice for a brokerage boat to have all this, as I thought it would only be dealer owned boats.

Re the OP and just out of interest, did anyone have a view or experience with the Euro Yacht Brokers warrantee? I guess that as a brokerage boat it is a bit of a bonus?

 

[rafiki_]

F

Exhaust outlet through hull means a very short run of pipe, it also eliminates the down angle problem from the riser or elbow as many boats require an "up" from the turbo before it can drop so not to allow sea water back in the turbo.

A direct drop is easy straight out into a silencer which on most boats I've worked on is moulded to the hull.

This set up always makes me question in my own head and there all "Ifs" but should the moulding delaminate away from the hull your going to let water in, I've seen a few boats having gel repairs in this area where over years a problem has started, mainly Azimuts so I'd check yours Rafiki, water stains and rust marks seem to appear.

The other downside is that you have sea water a lot nearer your turbo with salty air and no way of blocking it off unless you remove the exhaust elbow, this will corrode the turbo housing and vanes, which is the norm on most sterndrive installation...

Elessar you could fit different risers and then the dustbin silencers in the engine bay, or copy a sealine 42/5 installation where it drops straight out the bottom .

VP, many thanks for the heads up. Will have a close look at the exhausts next time I am on board. I'm not aware of any hull issues yet on my Snazi, and checked the hull very thoroughly before purchase. However, you can never say never.

 

[baylabayla3288]

Interesting.

The exhaust noise on my boat is wearing. There are no silencers because of the aft cabin causing space issues.

I was looking to re route the exhaust and put silencers under the bed but it's a lot of work.

So why didn't sealine exit the exhaust underwater I wonder. What are the downsides, what type of skin fitting, and what's the bypass for (I could use the existing exhaust as a bypass with reduced diameter and an inline muffler I guess )

Later Sealine 43s do have underwater exhausts. There is an external duct molded a long the aft chine with a downward opening aft. Looks like an easy solution to retrofit.

 

[baylabayla3288]

My experience with the dust bin mufflers + above water exits on the Phantom 38 is that they are very silent at low and medium speeds but at higher planning speeds they tend to be noisy. I had plans to modify the exits to go under water but the recommendation is to remove the mufflers to avoid a risk of too much back pressure.

 

[Deleted User YDKXO]

I have no silencers. And no room for them in the engine bay. I'm familiar with halyard stuff I used it when I re engined my bayliner. They need a lot of space when you take the hose turns in and out into account.

I'd be surprised if you didn't have at least some inline silencers, possibly behind the furniture in the aft cabin. They look like big rubber pipes. On a previous boat I owned, a Turbo 36 (also a v noisy boat), I fitted some cowls over the transom exhaust outlets which routed the exhaust down below the waterline. They made a marginal improvement but in a choppy sea with the transom lifting in and out of the water, the exhaust noise would rise and fall as the cowls lifted clear of the water. If you're handy, possibly you could fabricate some cowls for your boat in stainless or grp?

 

[simonjames]

Sorry for the delay in responding the boat has standard shafts not ipc. The only thing that worries me is potential failure of a fitting to the exhaust and potential consequences ie flooding engine room etc.