Normally, performance wise, the exhaust can't be too large in diameter. However in a boat, standing water in the exhaust can roll into the engine when the boat pitches as when anchored in a seaway. In this respect, smaller is better because it will contain less water. 3" is fine for your engine and 2" if manufacturer allows.
The hose should slope down all the way to transom then there should be no standing water in the exhaust when stopped and no chance for it to roll into the engine.
So why, if 9-10" above the waterline do you see any water when you remove the hose? Are the mufflers holding it? There are mufflers available that don't hold water. Is the lowest spot not at the transom as it should be?
If the exhaust hose can be rearanged (or elbows raised) so it slopes continuously down to the transom, and the mufflers do not hold water, you are fine with 9-10" drop. If not, a waterlift muffler in the engine space, as shown in a previous post, may be the answer but waterlifts have their own criteria for installation. They must be able to hold all of the accumulated water in the system aft of them for one. They also can fill with water and overflow into the engine under certain conditions.
I would favor correcting the system without taller jacketed elbows because they are expensive and when they leak internally, water will go right into the engine. Your existing elbows could be raised using dry pipe fittings but would have to be wrapped (lagged) for fire safety.
In looking at your photos again, it seems that the installer used up all the drop (and then some) right in the engine space creating a low spot right there. N/G
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By Tom Burden, Last updated: 7/11/
Consider what can happen when a hose bursts. If you are lucky, you will only have nuisance repairs to electronics, engine or interior. If fate has it in for you, a defective hose can cause a stink if it&#;s the discharge of the head, cause a fire if it&#;s part of a gas line or even sink your boat if it&#;s connected to a thru-hull fitting. That&#;s why we recommend spending a little more on a high-quality marine hose that offers more durability and better performance in critical applications and why you should inspect your hoses frequently for signs of deterioration.
Your application will determine what kind of hose to purchase. Our selection of hoses encompasses most applications and is available in any length from a foot up. The following is a guide to match hose and application.
Raw water intake hoses ingest water from outside a boat to cool an engine, flush a toilet, cool an air conditioner or provide a fresh supply of water for fish in bait tanks. Use only hose recommended for &#;below waterline&#; connections. Depending on the application, raw water intake hose will have fabric, PVC or stainless steel spiral reinforcement that resists kinking and prevents the hose from collapsing when for example, an engine pulls a vacuum due to a clogged water intake screen. For engine raw water intake, we recommend Shield's Series-250 or Series-252 hose, both of which are reinforced with a metal wire helix to prevent collapse. For engine coolant circulation, Shields Series-135 hose, which is reinforced with polyester yarn spirals can be a good choice&#;however care must be taken not to exceed the minimum bend radius and the temperature rating of the hose. For an overview of hose applications, see the hose application tables below.
Drainage hose for cockpit, sink or shower needs to be flexible with strong walls and resistance against kinks and abrasions, but since they are under positive pressure, they generally don't require helical wire reinforcement..
Potable water hoses must be made of FDA-approved, non-toxic materials so they won&#;t cause bad taste in drinking water supplies. Pressurized freshwater systems must use reinforced hose to withstand pump pressure (approx. 40&#;60PSI). For fill and vent hoses in water tanks, extra-heavy-duty sanitation/water hose should be used, while reinforced rubber hose is the best choice for hot water up to 140°F.
Alternatively, you may use a reinforced vinyl hose reinforced with nylon braid. Examples include: Series 162 (polyester reinforced clear PVC hose), FDA approved; Series 140 VAC Standard (steel wire reinforced PVC hose); and Series 148 Multi-Purpose (vinyl helix hose) FDA approved, ideal for critical drain and fill applications.
Bilge pump hoses typically use corrugated polyethylene with molded cuffs because it is flexible, economical and resists oil, solvents and other waste that collects in the bilge. For better flow you should choose a hose with a smooth bore, abrasion-resistant cover and good anti-kink flexibility. Examples include: Series 148 Multi-Purpose (smooth-walled vinyl helix hose) FDA approved, ideal for critical drain and fill applications, and Shields Multiflex Hose (Series 141). Of the corrugated hoses, the best is Shields VAC Standard (Series 140) and Bilgeflex (Series 120).
Sanitation hose has to be tough, flexible and resistant to odors and toilet chemicals. Choose hose with a smooth bore, heavy wall and specifically labeled for marine sanitation use. There are two choices: white vinyl hose and sanitation hose. Both will eventually smell. We recommend only smooth interior wall hose because corrugated types trap waste and restrict flow. Rigid PVC does not pass odors but is stiffer and more difficult to route and does not connect directly to pumps and thru-hulls. Still it is possible to plumb part of the system with rigid PVC, switching to hose where necessary.
Reinforcement: Many hoses have reinforcement in the walls for strength and rigidity, and to prevent collapse or expansion under pressure. The reinforcements can be wire, yarn spiral or PVC/vinyl helix.
Burst strength: Hose used for discharge lines has to resist pressure. This so-called burst strength, measured in pounds per square inch (psi) depends on product design and diameter; small diameter hoses have greater burst strengths. Hose with multiple plies or helical reinforcement has greater pressure limits, which is important for pressurized water or exhaust applications.
If you are looking for more details, kindly visit marine wet exhaust hose.
Vacuum rating: Hose on the intake side has to withstand suction, a property that is measured with a so-called vacuum rating. Intake hose should have a vacuum rating of 20 or higher.
Temperature range: Mostly critical for engine cooling hose, but might also be important for pressurized hot water systems.
FDA-approval: Hose used in potable (drinking) water systems must be constructed from safe, non-toxic materials that are contamination- and corrosion-free.
Bend radius: For proper installation a hose should not be bent more than the minimum bend radius recommended by the manufacturer to avoid kinks and breakage. Especially important for sewage lines and bilge pump applications.
Sometimes a lubricant is needed to install a hose onto a fitting.
Hoses are sized by their inside diameter (ID). Hose fittings are labeled based upon the ID of the hose they fit. In other words, the outside diameter of a 1/2" barbed elbow is liable to measure slightly greater than 1/2", but it will fit 1/2" ID. hose just fine. Smooth bore hose is recommended for all applications, since corrugated hose can reduce flow by as much as 30%. Hose needs to be matched to the fittings on pump, through-hull, deck fill, tank, etc. See below for some sizing guidelines. Some popular diameters by application:
Marine hose clamps are stainless bands that compress hose around barbed fittings. They can be made from a variety of metals, but quality ones are all stainless steel, including the screw, band, and other parts. T-Bolt hose clamps are much stronger and have a 360° clamping surface. They are used in applications with high pressure, heat, vibration, or other severe requirements, like exhaust systems. Two clamps are recommended for below-waterline connections. Thru-hulls, hose lube & sealant, etc. may be necessary to make a hose fit and complete your marine plumbing system.
Contact us to discuss your requirements of marine toilet hose. Our experienced sales team can help you identify the options that best suit your needs.