There are three ways that sea water can be ingested into the exhaust system while towing a Ranger and Cutwater with the engine not running. The high speed thru hull pick-up, The exhaust outlet, The shaft log coolant hose attached to the packing gland going to the hose that discharges seawater to the exhaust elbow. The question, is this normal for a boat under tow to have water ingestion in the engine while under tow? My opinion is no it is not common. If it was common it would be on every Tow boat captains check sheet to confirm that all seacocks are closed, exhaust outlets plugged, and shaft cooling glands have a devise to restrict water flow while the boat is being towed. The engine manufactures in this case ( Volvo would have a warning sticker stating that if the boat is disabled and being towed the the following measures need to be done to prevent damage to the engine. A sail boat is a perfect example of a boat that has an engine and is being towed by wind all the time. The engines in the sailboats are installed low in the boat and have specific specifications as to water line inlets and outlets elevations to prevent water intrusion. Many have to use vacuum breakers to eliminate the water from backing up into the engine.
This is a quote from Steve D'Antonio Marine surveyor "In simple terms, antisiphon valves allow air to enter while preventing water under pressure from exiting the plumbing run, thereby “breaking” the siphon. Every engine, generator, head, and bilge pump needs a properly installed antisiphon valve (also called a siphon break) if they are ever below the waterline under any vessel attitude."
If an engine is installed lower than the water line or above the water line the engine install must meet or exceed the manufactures installation requirements during a worst case! Generators which do not operate much of the time while the boat is under way are commonly damaged with water ingestion if the properer manufactures installation guild lines are not followed. Main engines are not usually damaged as easily because for the most part they are running when the boat is moving. Engine manufactures still require an installation that will prevent water from ingesting into the engine when the engine is not running. This is not just for disabled towing. It is also when at anchor or at a dock when conditions are present that could cause water to be forced into the exhaust which is an open water channel to the engine.
Rangers and Cutwater hull designs incorporate a lower engine installation. There are positive reasons for this design. Look at the bottom of a Ranger or Cutwater inboard. It has an interesting bottom. When I was sanding the bottom of my Cutwater I have to say I was amazed at the design. I have never sanded a bottom of a boat with " that much going on" It looks like the design of a genius! This design allows for the motor to be placed low in the hull. The engine install needs to be done in a way that will prevent water entering the engine. The Volvo installation manual gives all the specifications that must be met in order to prevent water ingestion. I assume Fluid Motion followed theses requirements. Volvo is supposed to inspect the install.
One unique hull configuration that caught my eye on the Rangers and Cutwaters was the indent in the hull where the exhaust outlet is. There is also a "Hull Flare" in front of the exhaust outlet. My thought to this design, it is a relief at the exhaust outlet to reduce back pressure to the exhaust system while the boat is running. Does this also create a low pressure when the boat is being towed? I don't know . I do know that when I looked at the exhaust hose elevation on my cutwater I found it to be marginal when compared to the Volvo specifications. I already stated this finding in an other post. I did make adjustments to it and followed up with an email to Fluid Motion customer service and was told we have never had any issues with this install before it is fine. I can say I never had any issues with it. I was also never towed.
The water backing up from the packing gland coolant hose to the exhaust is a plausible condition but one that I had never heard of until reading about it from a Tugnut on this site. Normally the exact opposite happens when a vessel is being towed. The gland is damaged because of a lack of water to cool the gland. While the boat is being towed the prop grabs water and starts to turn. There is no cooling water present because the engine is not running and the gland is dry. The shaft turning the causes friction, heat and damages the gland. This is commonly known and it is advised to lock the shaft to prevent it from turning. Another issue while towing is damage to the reverse gear if the shaft is turning. Locking the shaft will help prevent this from happening too. Most Tow captains area where of this problem.
How many Ranger and Cutwater owners are aware of this issue? It seem to happen when ever a Tug or Cut is towed if powered by an inboard engine. I personally know a couple of owners that have had this issue but I have read of several more and there have been some other threads that deal with this issue from Tug owners that have experienced this exact issue in the past. Is this a Fault design in the Volvo Penta ? I know of both D3 and D4 engine that were damaged from this both installed in Rangers.
Here are a couple threads.
viewtopic.php?f=2&t=18097&start=0&hilit=sea+tow
This is one that the factory representative never gave any advise on restricting flow from the exhaust or packing coolant line just the seacocks.
Also read Bob Allens post to this thread.
viewtopic.php?f=2&t=7448&start=0&hilit=got+towed
This one Andrew commented on closing the sea cock but did not comment on the original thread that the damage was causued from the packing gland coolant line. This thread was from 2016 and involved a Yanmar engine. The boat owner of the thread stated that the muffler was full of water but stated it did not fill from the exhaust hose. It filled from the coolant line from the packing. My question to that is how does he know that was the only source of water intrusion?
The 29' and 31 Rangers and the C30 are still in production. The rest of the boats that have the potential to have this damage are no longer production boats. There are 100's of these boats out there in use and will be for many more years. It seems the only way a owner is to know of the design issue of theses boats and the potential of water intrusion if towed is through this forum. There are many owners of Rangers and Cutwaters that never follow this forum and if they did they still probably would never know about this as an issue. Boat US has a consumer protection program. Having the boat manufacture or a boat owner contact Boat Us and explain the issue with theses boats and send a service bulletin out to Tow Boat US and Seatow may help save theses boat owners from the possible damage that may occur if towed.
Having to replace an engine because of not knowing the possibility of damaging an engine while being towed should not be the fault of the boat owner. This is not a common issue in the boating industry in my opinion.