Seawind and PDQ's

[tomfl]

Originally Posted by Patman

SNIP

What kind of range can you get with twin outboards motoring at (i'm guessing here) 75% power?

SNIP

Depends on the conditions you are motoring in. I had to motor into a maybe 15 knot head wind and a 3-4 knot tide and needed to use both my 9.9 Yamahas to move at 4.5-5 knots. Normally I can do that using one at maybe 3/4 throttle in flat water and no wind.

Keep in mind a boat like a PDQ or Seawind with outboards has a much cleaner bottom sailing with the outboards raised out of the water. There may also be an advantage with the props being more to the middle of the boat than boats with an inboard.

The real question for me is how much will you be sailing as opposed to motoring. Can you wait for the right weather window and use the sails or do you have a time table forcing you to motor, and sometimes motor into the teeth of wind and current. If you can wait outboards are fine, if you have a schedule to meet you may need to get inboards with big fuel tanks.

[downunder]

Originally Posted by tomfl

Depends on the conditions you are motoring in. I had to motor into a maybe 15 knot head wind and a 3-4 knot tide and needed to use both my 9.9 Yamahas to move at 4.5-5 knots. Normally I can do that using one at maybe 3/4 throttle in flat water and no wind.

Keep in mind a boat like a PDQ or Seawind with outboards has a much cleaner bottom sailing with the outboards raised out of the water. There may also be an advantage with the props being more to the middle of the boat than boats with an inboard.

The real question for me is how much will you be sailing as opposed to motoring. Can you wait for the right weather window and use the sails or do you have a time table forcing you to motor, and sometimes motor into the teeth of wind and current. If you can wait outboards are fine, if you have a schedule to meet you may need to get inboards with big fuel tanks.

No one has alluded to the range of the outboards on a Seawind. Its not terrific but thats not an issue in some cruising areas.

[Factor]

The point is it rarely matters, after 5 years I have 320 hours on the engines, and I sail a lot.

Motor sailing - one engine running at half throttle, about 500NM range.
Two engines running motoring into crap,about 150 NM - but why would you do it for that long?

Of course you can always carry a bit extra, indeed I can plug the dinghy fuel tank straight into the motor. and I can fit 100 litres in the forward vented to sea lockers. Which doubles the ranges mentioned.

[SailFastTri]

To answer the OP I think you'll find outboards to be much louder and less fuel efficient when motoring the ICW. Some of the resonant noises and vibrations (not just primary engine noise) can also become very annoying, but those are generally boat-specific. (I test sailed a Maine Cat 30 a few years ago that rattled my brain when the twin Yamaha 8's ran). The other pros and cons have also been expressed quite well by others here.

I've had day sails about both boats you're looking at and they're both quite nice. But if you're thinking about longer range cruising or living aboard you'll find a boat designed/equipped with diesels better suited, IMHO. Not that outboards won't work, diesels will work better.

One major factor is the lack of availability of stable gas in the US. If you store large tanks of ethanol on a boat with fuel-sipping engines you're going to have phase separation and condensation issues. In the last 10+ years ALL my dinghy engine problems have been fuel related, and (because of this) my next dinghy outboard will be propane powered or electric...

Now, if you're asking about sails best? Different thread.

[thinwater]

Originally Posted by tomfl

Depends on the conditions you are motoring in. I had to motor into a maybe 15 knot head wind and a 3-4 knot tide and needed to use both my 9.9 Yamahas to move at 4.5-5 knots. Normally I can do that using one at maybe 3/4 throttle in flat water and no wind.

Keep in mind a boat like a PDQ or Seawind with outboards has a much cleaner bottom sailing with the outboards raised out of the water. There may also be an advantage with the props being more to the middle of the boat than boats with an inboard.

The real question for me is how much will you be sailing as opposed to motoring. Can you wait for the right weather window and use the sails or do you have a time table forcing you to motor, and sometimes motor into the teeth of wind and current. If you can wait outboards are fine, if you have a schedule to meet you may need to get inboards with big fuel tanks.

Are you saying 2 x 9.9s will taking you into 15 knots on flat water at 8.5-9 knots (that is the math)? I would think more like 7.5 knots. Big difference.

[thinwater]

Unstable gas is trouble--Another myth. I've only run e-10 gas for 20 years, because that's how long we've had it in my region.

The simple answer: a vent filter will keep the water vapor out. Automotive systems are not open (they breath through carbon) and new boat systems do the same. It also saves gas, specifically the high value volatiles.

Sail Delmarva: Gasoline Tank Vent Filters--Better Boat Keeping?
Sail Delmarva: Gasoline and Fuel Tank Vent Filters

Alternatively, just keep the tank full when not in use to limit breathing. This is good practice with any fuel tank. With the dingy, fill the tank AFTER using, instead of before, and close the built-in vent when not running.

None of this is difficult, it just requires some diligence in a marine environment.

[tomfl]

Originally Posted by thinwater

Are you saying 2 x 9.9s will taking you into 15 knots on flat water at 8.5-9 knots (that is the math)? I would think more like 7.5 knots. Big difference.

You must be using that new math I keep hearing about.

What I said was motoring into a head wind and against the current/tide was slower than motoring with no wind and no tide. At 3/4s throttle a boat is not always going at 3/4s of the boat's top speed; the relationship is not linear. The fastest speed I have seen on the GPS is around 6.9/7 knots in flat protected water. But the boat goes about that fast with light wind and maybe 1-2 foot waves.

I suspect the boat might go a little faster in flat calm water with smaller props with outboards that were not high thrust, but would suffer a drop in speed in more adverse conditions.

As Factor said Seawinds are much better at sailing than motoring. I expect double digit speeds if the wind is over 15 knots and am often shocked at how fast the boat is with its big square top and flat cut screecher that maybe gives up a little off the wind but really helps sailing closer to the wind, something that happens frequently when the boat speed shifts the apparent wind forward.

I am frequently passed by condomarans motoring out of the harbor, it is maybe a mile or so to open water. But once the sails are up a Seawind is a joy to sail.

[sandy daugherty]

I own both. Siesta, my Chris White Atlantic 42 has two Yanmar 27 HP 3GM30s. My PDQ 36 has two Yamaha 8 HP High Thrusts. The PDQ is 1.5 Knots slower than the Atlantic, and burns more fuel. That's OK since there are more places to buy gasoline on the East Coast, the Bahamas, and the Caribbean. Net difference = zero.

I carry fuel for Siesta's dinghy in plastic Jerry Cans, But can fuel the PDQ's dinghy from the much safer main tank. That would make the purported hazard of gasoline the same, if there really was a hazard. Statistically, none exists for bridge deck cats.

There are no 30 HP outboards that are as fuel efficient as Yamaha's High Thrust 8s and 9.9s. They are all geared and propped for max power in the 15 to 20 knot range of speed thru the water. Thirty six or seven feet LOA, and 10,000 pounds cruising weight is the upper limit for twin outboard engines on cruising cats that want to go seven knots. They key here is to find an outboard engine that reaches its rated power at the optimum cruising speed of the vessel. Putting bigger motors on a cruising cat does not equal higher speed, while pushing into wind and waves just wastes more gas (and life expectancy) as the higher boat speed motors ventilate or cavitate, or both!
There are lower power diesels that are perfectly suited to cats under 10,000# and 38' over all, they are quite expensive and much more difficult to work on down in a hole than an outboard is when its sitting in your lap. This advantage doesn't apply to outboard motors over 30 HP, so for the time being, bigger Production cats can't use outboards. This is a shame, because four consecutive outboards are cheaper to buy run, and maintain than a diesel, which costs more than four times the installed price of an outboard, and has a reasonable life expectancy of less than those four outboards. Add the cost of folding props to the diesel, and the argument is moot. Net difference earns a point for the outboards on a lighter cruising cat.

Cruising cats sail. If they didn't, they couldn't reach many of the places we want to go. Outboards (and sail-legs) lift out of the water, but diesel cats drag a lot of hardware in the water when they are sailing. The PDQ 36s with diesel engines are a bit more than a knot slower than the outboard versions, which were more popular by a 3:1 ratio. net difference = another point to outboards.

Diesel motors can turn really big alternators, yielding lots of amps for electrical appliances. We often overlook the fact that those alternators rob a lot of horsepower from the 'prime movers'. That fact needs to be included on a comparison spreadsheet. Outboard motors put out enough amps to recharge their starting batteries, run some lights, and a GPS. That's OK because there really isn't room on a mid-thirty-foot cruising cat for washing machines, dive compressors, and ice makers.

This is where we insert the tie-breaker; the portable 2000 - 2500 watt gasoline generator. My Honda eu2000i recharges the house batteries, runs the microwave, the coffee pot and the air-conditioning just fine, sips gas is not very loud, but IS very reliable. Net score = outboards (and a portable generator) win every time.

But there is one criteria remaining, powering into adverse wind and seas. I have two experiences to relate.

1. On the PDQ 36 we were caught in a sudden Chesapeake squall. The genoa tore out. We sailed on the main until we reached the river to return home. The wind was blowing 30 and gusting to 40, with short period 4' waves straight down the river. Tacking was out of the question. I fired up the two elderly 9.9 HP Yamahas that I had been nursing along for two years, set the throttles at full, and pointed home. We made 1 or 2 knots into the eye of the wind. We continued to make way up river until the surrounding trees and cliffs provided enough shelter to finish the trip. Five other boats, monohulls from my sailing club had to turn back, and anchor out half the night.

2. Heading south with the Caribbean 1500 on Siesta after a hurricane plowed its way up the Coast, we tried to hug the coast to avoid the Gulf Stream and its tailwind. We headed east to clear the Shoals of Cape Hatteras we found ourselves in some very uncomfortable weather, at night. The Port engine (not the critical engine) quit and would not start. We spent two exhausting hours trying to get the main down, because we couldn't hold into the wind. This experience would have been avoided if there had not been a bit too much wishful thinking in the decision to press on.

The moral of these two stories is this: a smaller cat with outboards can handle serious adverse weather without over taxing the crew. Sometimes. a knot is enough. And the best equipped vessel can't handle the worst that can come from poor seamanship.

To finish the Cape Hatteras story, we go the main down to the third reef, and motor-sailed to the Charleston Harbor entrance, took a tow from TowboatUS, and spent 4 days licking out wounds before continuing the trip. We had straddled some Hurricane debris and partially flooded the engine room through a hole almost 5 feet above the waterline!

All the planning and preparation in the world cannot surmount what Mother Nature can dish out, but do your best to keep her happy.

[sandy daugherty]

[QUOTE=tomfl;1573811]
I suspect the boat might go a little faster in flat calm water with smaller props with outboards that were not high thrust, but would suffer a drop in speed in more adverse conditions.

QUOTE]

To put the most thrust into the water, use a slow turning large diameter propeller pitched and geared to allow the engine to reach its peak on the power curve, and don't let it ventilate (suck air) or cavitate (make steam from grossly overpowering a propeller.

Outboard motors sell better if they can push a boat faster. People make buying decisions based on horsepower claims but fail to understand that power comes at a particular rpm. If the gearing and propeller measurements prevent the engine from reaching that rpm, it provides less (sometimes much less) power to the prop that converts rpm to thrust. Significantly, the boat must also be moving through the water at a sufficient speed for the prop and gear to allow the engine to operate at that optimum RPM.

More simply, the boat must be moving fast enough to allow the engine to reach its advertised power.

Boats that don't plane have speed limits. The power required curves shoot upward requiring gobs more power to go a tiny bit faster. The narrow hulls of sailing catamarans don't break that law, they just stretch it a good bit. They still require a lot more power (think two or three times more horsepower) to go a bit faster (think fractions of a knot.)

Most people buy motors in the 10 to 30 HP range for light craft, capable of being driven 15 to 20 mph by a motor under 130 pounds. With two exceptions, all outboards are propped for that speed. Only an insignificant segment of the motor buyer population ride in boats that won't go more than 10 mph.

Those two exceptions are the Yamaha High Thrust 8.0 and 9.9 horsepower engines. All manufacturers (including Yamaha) have outboard engines advertised as Thrustier, Bigger footed, or something else, where they have bolted on a different pitched prop, and slapped on a big decal. Yamaha built a power-leg with room for a larger diameter prop, and bigger gears. These two engines have almost a 3:1gear ratio, Every other motor is geared closer to 2:1, a big whopping difference. Yamaha equips these engines with props that let the power-head reach its max power at something like 10 MPH. That's another whopping difference.

In fact, the Yamaha 9.9 produces more Full Throttle thrust at 10 mph than a Honda 20 at the same speed. The same motor will push a Gemini 3000 just as fast at a Tohatsu 40 HP two-stroke from the 1980's.

So if you want to go a little faster on a 30 - 37' cat, add wind.

[44'cruisingcat]

[QUOTE=sandy daugherty;1576093]

Originally Posted by tomfl

I suspect the boat might go a little faster in flat calm water with smaller props with outboards that were not high thrust, but would suffer a drop in speed in more adverse conditions.

QUOTE]

With two exceptions, all outboards are propped for that speed. Only an insignificant segment of the motor buyer population ride in boats that won't go more than 10 mph.

Those two exceptions are the Yamaha High Thrust 8.0 and 9.9 horsepower engines. All manufacturers (including Yamaha) have outboard engines advertised as Thrustier, Bigger footed, or something else, where they have bolted on a different pitched prop, and slapped on a big decal. Yamaha built a power-leg with room for a larger diameter prop, and bigger gears. These two engines have almost a 3:1gear ratio, Every other motor is geared closer to 2:1, a big whopping difference. Yamaha equips these engines with props that let the power-head reach its max power at something like 10 MPH. That's another whopping difference.

In fact, the Yamaha 9.9 produces more Full Throttle thrust at 10 mph than a Honda 20 at the same speed. The same motor will push a Gemini 3000 just as fast at a Tohatsu 40 HP two-stroke from the 1980's.

So if you want to go a little faster on a 30 - 37' cat, add wind.

Wrong in so many ways I don't even know where to start...

[Dulcesuenos]

Actually a lot of it is correct. We put a 40 HP Ob on a cat that came with a 25 stock and no custom large lo pitched prop in the world would make the boat go more than half a knot faster than The 25 HP. The motor did turn slightly slower rpms at same speed but consumed same amount of fuel. But doubters will doubt. It comes down to gearing, and hydro dynamics. Tried explaining this before but until someone wastes the money and eats crow they don't believe it.

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

[smj]

Originally Posted by Dulcesuenos

Actually a lot of it is correct. We put a 40 HP Ob on a cat that came with a 25 stock and no custom large lo pitched prop in the world would make the boat go more than half a knot faster than The 25 HP. The motor did turn slightly slower rpms at same speed but consumed same amount of fuel. But doubters will doubt. It comes down to gearing, and hydro dynamics. Tried explaining this before but until someone wastes the money and eats crow they don't believe it.

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

There's no doubt when you reach the "theoretical" hull speed of a generic cruising cat it will take a lot of power to get above that speed but it can be done. The Carlson 32 would do over twenty knots with twin 90 hp and there's a poster here who has a 38' cruising cat with twin motors that are over 100 hp each that can reach 20 kts.


Sent from my iPad using Tapatalk

[SailFastTri]

Originally Posted by sandy daugherty

snip1
2. Heading south with the Caribbean 1500 on Siesta after a hurricane plowed its way up the Coast, we tried to hug the coast to avoid the Gulf Stream and its tailwind. We headed east to clear the Shoals of Cape Hatteras we found ourselves in some very uncomfortable weather, at night. The Port engine (not the critical engine) quit and would not start. We spent two exhausting hours trying to get the main down, because we couldn't hold into the wind. This experience would have been avoided if there had not been a bit too much wishful thinking in the decision to press on.

The moral of these two stories is this: a smaller cat with outboards can handle serious adverse weather without over taxing the crew. Sometimes. a knot is enough. And the best equipped vessel can't handle the worst that can come from poor seamanship.

To finish the Cape Hatteras story, we go the main down to the third reef, and motor-sailed to the Charleston Harbor entrance, took a tow from TowboatUS, and spent 4 days licking out wounds before continuing the trip. We had straddled some Hurricane debris and partially flooded the engine room through a hole almost 5 feet above the waterline!

All the planning and preparation in the world cannot surmount what Mother Nature can dish out, but do your best to keep her happy.

Sandy, that was an excellent post, especially the part I snipped (only to save repetition).

With regard to the quoted part above, I'm curious about what type of sail track was used on that boat. I consider a low-friction sail track and full-battens to be essential safety equipment on any multihull, because that's the only way you'll be able to lower the main while running downwind when overpowered.

If you can't reef while running, and heading up is required to reef, then there's no way to safely do so without increasing apparent wind. As an example; if you're overpowered and running, and boat speed is ~10 knots, rounding up will increase apparent wind by a minimum of 10 knots and likely much more. That can set the stage for a capsize or pitch-pole. (Most multihulls would likely be sailing in the teens if running overpowered, so this example is very conservative.)

[tomfl]

[QUOTE=sandy daugherty;1576093]

Originally Posted by tomfl

I suspect the boat might go a little faster in flat calm water with smaller props with outboards that were not high thrust, but would suffer a drop in speed in more adverse conditions.

QUOTE]

SNIP
Those two exceptions are the Yamaha High Thrust 8.0 and 9.9 horsepower engines. All manufacturers (including Yamaha) have outboard engines advertised as Thrustier, Bigger footed, or something else, where they have bolted on a different pitched prop, and slapped on a big decal. Yamaha built a power-leg with room for a larger diameter prop, and bigger gears. These two engines have almost a 3:1gear ratio, Every other motor is geared closer to 2:1, a big whopping difference. Yamaha equips these engines with props that let the power-head reach its max power at something like 10 MPH. That's another whopping difference.

In fact, the Yamaha 9.9 produces more Full Throttle thrust at 10 mph than a Honda 20 at the same speed. The same motor will push a Gemini 3000 just as fast at a Tohatsu 40 HP two-stroke from the 1980's.

So if you want to go a little faster on a 30 - 37' cat, add wind.

There are two factors to consider in determining how fast a motor will push a boat. The first is the RPM the prop is spinning. The second is the thrust the prop generates.

As long as the thrust generated is greater than the friction stopping the boat from moving through the water the boat will go faster with a higher RPM.

A smaller prop will not generate as much thrust as a large prop (assuming the props were not designed by a moron) but will spin at a higher RPM with the same amount of power.

The fly in the ointment is the friction stopping the boat from moving through the water. In flat calm water this friction is a function of boat speed, but wind and current can increase this friction. The trick is to get the right compromise of prop size (and number of blades) for the best thrust and RPM combination. Reducing the number of blades and size of a prop will increase RPM (and potential top speed) as long as the thrust is sufficient to overcome the friction. Problem is when you are motoring into wind and current the thrust may not be enough to overcome the additional friction.

In a boat like a Seawind/PDQ with a real high thrust motors the compromise is biased to provide more thrust at the expense of a slightly higher top speed in flat calm water.