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Tunnel Drive Coweling Installation

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joremi

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"I'm installing new coweli

"I'm installing new cowelings on my twin tunnels. I have chaulked them both with 5200 and have had a significant drop in high end power. Upon inspection, the exhaust port alone seem too small. Should I NOT chaulk the cowelings and allow exhaust to exit all around the bottom of the coweling? Has anybody had experiend with this before?"
 
"Not enaugh info.
Make any ot

"Not enaugh info.
Make any other motor changes?
High end power means? Top speed, hole shot??
What is the rpm's of wot now compared to before?"
 
Thanks for responding. Both e

Thanks for responding. Both engines were rebuilt this summer. Up until recently both ran identically: 35-3700rpm @ 24 knts. The only change made since then is the replaced cowlings. Now both engines struggle to get to 3000rpm @ 14 knts. Idling and slow speeds (1500rpm @ 7 knts) is not a problem.

The cowlings were leaking exhaust and water around their seams and they were beginning to break up as they were being pulled away from the stern. I purchased new cowlings and sealed them well. Now the exhaust must exit the hole at the rear of the exhaust plate. The hole does not seem big enough to me. There are two 3 and ¼ hoses leading into the cowlings and the exhaust port it only about 3” x 2”. So I’m wondering; maybe the cowlings should have never been sealed with 5200? Maybe they are supposed to leak exhaust and water? I don’t know what else to think. Any thoughts?
 
"When you refer to twin tunnel

"When you refer to twin tunnels are you talking about 2 identical tunnel boats or one boat with 2 tunnels? (OLD sroke boy here, sometimes needs more detail..sorrry)
Other than that, something has changed between before and now. You indicate engine exhaust port is now smaller? If it is smaller, it could restrict exhaust and that would slow engine top speed and acceleration."
 
"I'm talking about two tun

"I'm talking about two tunnels on the same boat. This maybe only charactereistic of Penn Yan and unless you've seen it it's hard to explain.

It's not that the exhaust ports are smaller; they are fixed and can not be changed. However, they look small to me and since exhaust can no longer escape out of the seams of the cowlings. My question is, should these cowlings be chauled in the first place?

Thanks for your help."
 
"I have owned two tunnel boats

"I have owned two tunnel boats, 17' outboard and 24' v drive. Never messed with the hull but the sponsons on my boats were not meant to be anything but water tight even though on the v drive, each sponson had a exhust port.
Considering there are other design possibilites, I am now going to bow-out because I have no experience on your particular boat design."
 
Thanks for trying. Some of th

Thanks for trying. Some of the prob could by my own wording.

One last question: what's a sponson?

Thx
 
"First, I might say, my first

"First, I might say, my first tunnel boat was 17' powered by outboard with speed around 55mph which was too squirly so I went to the longer boat which tried to kill me at 70+, end of my tunnel boat life.
The high performance tunnel boat as I viewed them on show room floor were nothing but sport versions of hydroplanes. They have a "sponson" or planing surface on each side of the boat which forms a single tunnel down the center. I am assuming this is the "cowel" you are refering to? On plane, the boat rides on the lower or bottom of "sponson" and somewhat supported by the thrust of the prop at the center stern. However there are large cruisers with the same type of design but not intended for the insane speeds. As for many hull designs and water tight integerity, I do not know.
As for water tightness, I have a hard time figuring why anything in the water would be intended to leak because what leaks out in exhaust gases, can leak in as pure H2O.
As I said there are many designs out there and who knows, maybe one is intended not to be water tight, I've seen some wierd stuff over the years. As for a double tunnel, I have not seen but can easily emagine the configuration.
A very basic tunnel boat is a pontoon boat and a very large tunnel boat could be a cat, its all in the eye of the beholder and new termonology. Again, I have no clue on your design so again I bow-out.
Pausing to take a breath.........
Are you sure that you have not restricted your exhaust in some manner? Your symptoms indicate it. Or they filling up with water and depending on size of boat, you are trying to plane a extra half ton of water?
Sorry if Im no help"
 
"I am familiar with penn yan.

"I am familiar with penn yan. to those who are not, it is not a tunnel boat. it is a tunnel drive. the prop and shaft ride in a tunnel. some old sea rays used this design. it is an inboard. other than that Joe, I don't have the slightest idea what you are talking about. what "cowlings" did you replace?"
 
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