Dinghy Drag

[jibes138]

Towing a dinghy causes a lot of drag that on a long run increases the trip significantly. I'm thinking of ways to allow you to get the dinghy out of the water to reduce the drag and yet still be towing it. A couple of thoughts are using hydrofoil wings to lift the dinghy out of the water, does anyone know the drag difference between hydrofoil wings and the dinghy? The idea is to get the dinghy up on a plane but at low speeds. These flat bottom skiffs take very little energy to push along, so maybe a kind of sled that will plane the dinghy instead of pulling it through the water. Any ideas out there?

 

[Maine Sail]

Towing a dinghy causes a lot of drag that on a long run increases the trip significantly. I'm thinking of ways to allow you to get the dinghy out of the water to reduce the drag and yet still be towing it. A couple of thoughts are using hydrofoil wings to lift the dinghy out of the water, does anyone know the drag difference between hydrofoil wings and the dinghy? The idea is to get the dinghy up on a plane but at low speeds. These flat bottom skiffs take very little energy to push along, so maybe a kind of sled that will plane the dinghy instead of pulling it through the water. Any ideas out there?

To minimize drag you can adjust the bridle so it tows on the stern wave and surfs it. It reduces drag of the dinghy tremendously. I can hold my RIB easily with one hand, and not even a tight grip, when surfing, but it takes a very strong grip to hold it when not surfing.. I adjust mine with each change in hull speed to keep her surfing. Otherwise, I just put it in the davits...

 

[Roger Long]

Towing a dinghy causes a lot of drag that on a long run increases the trip significantly.

Here's the actual amount under power for a 32 foot boat from sea trials on mine. I got the first set of data, cut the dinghy loose to drift, and retook the measurements in the same conditions. Whew. It's amazing how fast even an 8 foot dinghy becomes just a speck in the water. Pretty sobering exercise if you think about looking for a head.

 

[druid]

One comment: keep the dinghy as light as possible. remove the motor, fuel tank, battery... anything else you can. (Probably a Good Idea to remove the motor anyway in case the weather gets snotty)

druid

 

[Dragon]

Main Sail...why do you tow your dinghy when you have davits?

 

[Maine Sail]

Main Sail...why do you tow your dinghy when you have davits?

Cause they are a PITA some times. If we need to make time, I will hoist it, but if we are gunkholing, and not concerned about speed, most of the time we tow. I basically use them when the boat is on the mooring to keep the RIB out of the water. Davits are nice in calm conditions but are not good for rough weather. In anything over 4 foot rollers but under 10 foot I'll tow, beyond that she goes on deck..

 

[Bill Roosa]

Other considerations

Putting the dingy on deck can cause visability issues. My GF is 5' and if we put the dingy forward on deck she can't see the water to forward when at the helm. Got her a box to stand on but it had sliding issues. Did some davit calculation and figured out that she could not see to aft if we went with davits. We tow all the time but will have to get a bigger boat when we decide to go off shore :dance:
FWIW

 

[Joe]

Putting the dingy on deck can cause visability issues. My GF is 5' and if we put the dingy forward on deck she can't see the water to forward when at the helm. Got her a box to stand on but it had sliding issues. Did some davit calculation and figured out that she could not see to aft if we went with davits. We tow all the time but will have to get a bigger boat when we decide to go off shore :dance:
FWIW

If you had a taller girlfriend you could go offshore now. Heh, heh.

 

[Stu Jackson]

If you had a girlfriend who could stand on the side of the wheel and look around the dinghy...

 

[Bad Obsession]

If you are extremely concerned with drag and going fast, use an inflatable dingy and store it in the boat when not in use OR buy a powerboat. LOL.

Seriously, you loose a little speed to a dingy but it is okay because you are just cruising and there are no time limits or people to race. Yeah, I do have to remind myself of this as I use to race, but these days I don't mind going a little slower. You still get there.

 

[Roger Long]

I don't mind going a little slower. You still get there.

I was coming back from a long solo cruise last fall and I told my girlfriend that I would dock at 12:30 when I called her in the morning. Since she wouldn't be able to see me coming up the harbor, I thought it would be fun to come around the bridge pier at exactly 12:29 and touch the dock precisely at 12:30.

I was under power and using the GPS route ETA displays and I was about 5 minutes early an hour out. I started backing off on the power. It is amazing how much you have to slow down to make just a small difference in your arrival time. I couldn't stand the feeling of going so slow when I was ready to be home so I ended up sitting in the inner harbor for a few minutes before heading through the bridge.

 

[Tom Spohn]

This looks like a possibility:
http://www.dinghy-tow.com/

 

[sailaway78]

Looks like very little loss

From looking at Rogers graph, doesn't look like much speed is lost towing. Maybe 1/4 knot. I don't know about you, but I have never been in that big of a hurry. Standard practice for me is to tow when inshore, and put it up on deck when offshore. I would highly recommend installing eyes on the transom, and using these as a base for a bridal. Is a much stronger setup than just the D rings on the dink.

 

[Sumner]

.......... I would highly recommend installing eyes on the transom, and using these as a base for a bridal. Is a much stronger setup than just the D rings on the dink.

Thanks, I'm going to look into that and try it out. I'm wondering how it will work with the outboard on. Right now without the outboard.................

..................the dingy pulls real nice.

But when the outboard is on.................

.............it pulls with the bow up due to the outboard weight in the back. I wonder if I experiment with the back attach points if I can help that situation out. With the side tubes sticking out the back how do they run the line so as to not chafe the tubes? I'm thinking that might be a problem.

We normally don't have the outboard on the dingy, but on........

http://purplesagetradingpost.com/sumner/macgregor/outside-12.html

.... a mount on the Mac. When we go to Florida next year I would like to have the outboard on the dingy most of the time. One thing that hasn't helped is that we got a long shaft outboard for the dingy so that we would have a spare for the Mac and I.....

http://purplesagetradingpost.com/sumner/macgregor/zodiac-3.html

...... raised the transom to move the long shaft up higher. I talked to Zodiac before I did this and the guy felt it was a good idea with the 5 HP we are using. I think the additional 5 inches in height of the motor is providing more leverage that is not helping with the way the boat rides.

c ya,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

 

[Scott B]

Cause they are a PITA some times. If we need to make time, I will hoist it, but if we are gunkholing, and not concerned about speed, most of the time we tow. I basically use them when the boat is on the mooring to keep the RIB out of the water. Davits are nice in calm conditions but are not good for rough weather. In anything over 4 foot rollers but under 10 foot I'll tow, beyond that she goes on deck..

You tow? between 4-10 ft.? I was in 4-6 ft. following, last summer and was nervous with the dinghy surfing sideways down each wave. Although, I don't have a choice yet, without davits installed.

 

[Ron20324]

I'm always looking for things to do dual-duty. My Maestral dingy came with 2 u-bolts on the transom (AND the hard bottom). I removed one of the nuts on each u-bolt and put an eye-nut on. Another attahment point for whenever something might come up. If I was starting from scratch, I suggest using eye bolts on the transom with fender washers or bigger, then an eye nut to secure it all.

 

[sailaway78]

No problem with chafe

I run the painter from the stern towing eyes, through the towing D rings. It pulls in just about the exact same attitude as towing just from the D rings. I never tow with the engine mounted, so can't give you any info on that, but it should be about the same as it is when pulled from the D rings. I have had no problems at all with chafe.

 

[Sumner]

I run the painter from the stern towing eyes, through the towing D rings. It pulls in just about the exact same attitude as towing just from the D rings. I never tow with the engine mounted, so can't give you any info on that, but it should be about the same as it is when pulled from the D rings. I have had no problems at all with chafe.

Thanks. Can you see the gas tank at the back in the picture? It is red u-shaped sticking up on both sides of the transom. Do you come from there inside the boat parallel to the tubes forward and then down over the tubes at the bow sides to the D rings?

I'm thinking of maybe using straps in that area to maybe just in front of the D rings, but maybe they aren't needed.

Thanks,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

 

[Ron20324]

Where are your d rings on the side tubes? top? sides? bottoms?

 

[Maine Sail]

You tow? between 4-10 ft.? I was in 4-6 ft. following, last summer and was nervous with the dinghy surfing sideways down each wave. Although, I don't have a choice yet, without davits installed.

Most of the time unless it is the fast growing short steep stuff... You need a long painter and I also drop my Davis Pellican Wheels to prevent surfing... Works like a charm.. They create enough drag so the dink behaves quite well with no surging, snapping or tugging. When going down wind the added drag of the wheels can be useful..