Dinghy survey

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thinwater
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Re: Dinghy survey

Post by thinwater »

I posted this some time ago:

http://sail-delmarva.blogspot.com/2010/ ... s-she.html

I will admit I made some pretty conservative assumptions, but I think they amount to a normal safety factor.

Personally, I think that weight is pushing it. You need to add for snow load, filling partly with water due to a wave break (happened to me once), dynamic ups and downs in rough weather, and other horsing around. Certainly, some sailors mount heavy motors and get away with it for many years, but they are cutting deeper into the safety factor. You state that you believe the heavy end is about 150 pounds plus external fuel tank and other items, unless it is worth emptying the tender after each use.

Perhaps the simplest answer is this; take someone's hand, walk out the davit, and jump up and down on the very end of the davit, which will be a fair approximation of the dynamic load the davit will see. If that seems like abuse of the structure, it is too much. When the boat was built, a 6hp 2 stroke and soft floor was the norm, and she was well designed for that. Your considering carrying a real boat.

She is also going to be a bear to hoist (like hoisting a person) and getting the motor off the boat and onto a bracket is asking for a back injury. For gosh sakes, a 9.9 is one of your main engines, and I have replaced them. Yes, to really plane with 2 people + gear you may need that much, but there is a trade-off. I have a 3.5 hp 2-stroke with a sport boat bottom. It will just plane with one person. I think 6hp is about right if you want zip, though I seldom use more than 2 hp.

http://sail-delmarva.blogspot.com/2009/ ... n-pdq.html

Also, check the length very carefully; I am not at my boat, but my 9' boat is a very close fit. But manufacturers may vary.

Always compromises....
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maxicrom
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Re: Dinghy survey: Davit Weights

Post by maxicrom »

F & K,

Our PDQ 36 has after market davits, very expensive Kato Marine units that came with the boat. As mentioned earlier in this post we have a 9ft (actually 8' 6") Zodiac active V high pressure inflatable bottom it weighs about 60lbs - with a Yamaha 4 cycle 8hp about 90lbs it overloaded our davits. I made new mount plates with side bracing to allow for a stronger angle and long story short we switched to a 3.5 2 cycle Yamaha outboard at 28 lbs - about 80 pounds is a good safe weight we can travel with. Our problem is the rear rail which supports the davits is just not strong enough for the weight plus rough conditions. There are solutions such as removing the motor - I'm fairly strong at 6' and 250lbs and manhandling a 90lb motor to a floating dinghy is a bear (hint: always attach it with a rope in case it falls in the drink, nothing worse than retrieving a $2000 motor out of the muck). Also, lifting the 3hp \ dinghy combination is a breeze with the double blocks that came with the davits. With the 8hp it's a workout and possibly over the limit for the block size. We've run the 8hp on a friends 10' Avon RIB and it planes much better than the 9' Active V soft bottom - like anything it's a matter of choice (but the Avon weighs in at over a 100lbs). The 3hp putts along just fine though it's a bit underpowered in weather and you have to resolve to observe while others are planing about. We had considered a smaller 6' RIB but with 2 dogs, the 2 of us, gear, and the occasional passenger it was just too small.

Hope this helps, good luck...

Mike

FYI: Eventually I plan to build a radar arch to replace the rear rail and davits and design it to support the larger motor. Linda really wants the aft bench like on the later models. II the Max has a single Yanmar diesel aft on the port hull and an 18 gal holding tank in the other making for a heavy stern. With that the 39' extension project looks like a something for the future to combine with the new arch.
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fredandkathy
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Re: Dinghy survey

Post by fredandkathy »

Thank you thinwater and Mike for the excellent advice.I did some measurements and the 9'6" length will just fit. Still concerned about the weight so I'm still discussing options with the dealer. Stepping down a bit, they also have an 9' AB aluminum RIB that is 80 lbs (about 25 lbs less than the 9'6") and would fit better. With the 8HP Yamaha at 83lbs + gas tank and small anchor forward, total weight is probably about 180. I could minimize the hoisting issues with a bigger block in the stern as I do not want to have to remove the engine to raise it. I think the stern would weigh about 120 lbs dry, about 60 lbs more than my current dinghy & 2HP motor. No worry about snow weight, ever! I'll keep checking this before making any decisions though. Fred
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eepstein
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Re: Dinghy survey

Post by eepstein »

To provide another view of weight. I have an Avon RIB at 140lbs + 8hp Merc at 76 lbs and have many times stood in the boat on the davits, as well as use it for gear storage when underway. It also sat full of water once. I am not sure what the construction of mine is, vs what you are looking at. Just wanted to let you know.
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mikeandrebecca
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Re: Dinghy survey

Post by mikeandrebecca »

We upgraded to a 8.5' RIB and a 9.9 HP 2 stroke yahama. We love them, BUT, we have been struggling with getting them to sit securely on the davits. I am not so concerned with the weight but we can't seem to get it high enough out of the water. It seems we will have to remove the engine from the dinghy. This is a bit of a PITA but we did it today using the main sheet/boom. We welcome other suggestions.
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eepstein
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Re: Dinghy survey

Post by eepstein »

Mike;
If you look at the attachment points at the top of the davits on Desert Star, you can see that they moved them aft of the frame to get the dingy farther out and more space. Perhaps you can get a welder to do that on yours (?)
BTW - Joey and Christine on Bright Eyes (http://svbrighteyes.blogspot.com/) just got to the entrance to the dismal Swamp Canal this evening. They are following your bread crumbs...
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amytom
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Re: Dinghy survey

Post by amytom »

mikeandrebecca wrote:We upgraded to a 8.5' RIB and a 9.9 HP 2 stroke yahama. We love them, BUT, we have been struggling with getting them to sit securely on the davits. I am not so concerned with the weight but we can't seem to get it high enough out of the water. It seems we will have to remove the engine from the dinghy. This is a bit of a PITA but we did it today using the main sheet/boom. We welcome other suggestions.
We've had the same problem. I've been considering adding weaver davits to the side of the dinghy and the deck seam below the aft hatches. This would hold the side of the dinghy closest to the boat tight and the davits would only be holding up the other side. Still a thought in progress...
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mikeandrebecca
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Re: Dinghy survey

Post by mikeandrebecca »

I love the arch on Desert Star.

We have struggled with so many variations trying to secure it better. We have tried using other lines through blocks led to winches. We run dock lines under it as Drew suggested. Part of the issue with this particular dinghy is that the attachment points on it seem higher than the ones on our old Walker Bay dinghy. Because of this, we lose at least 4-5 inches of height.

I wrote a bit about this on our blog today:

http://www.zerotocruising.com/?p=8883
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Re: Dinghy survey

Post by fredandkathy »

Mike & Rebecca - What is the combined weight of your new RIB & motor, if you know? The location of the davit lift points is also a problem for my current achilles, too high, requiring motor removal everytime, and as you say, a PITA, even though only a 2HP that is light, except on a wet and bouncing transom! The new RIBs I'm looking at all have lift davit points near the floor so there should not be a problem leaving motor on and raising it high enough. The PO installed a FORESPAR MOTOR MATE on the transom to lift O/Bs but I've never used it and don't know the weight lift specs. But i'm now looking into it because of my anticipated purchases. Fred
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Re: Dinghy survey

Post by mikeandrebecca »

The Yamaha 9.9 HP 2-stroke weighs 79 lbs (the tohatsu 4 hp 4-stroke that we previously used weighs 60 lbs). I don't know the weight of the dinghy but it is small. It is only 8.5 feet (hypalon RIB).

The cranes that I see advertised seem to be all rated for 100 lbs or more.

I would really love to NOT have to remove the engine. It is a PITA. With our old dinghy and outboard we never removed it.

I considered adding new attachment points in the transom but to gain any real improvement, they would be below the water line. Not so sure how I feel about that!
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thinwater
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Re: Dinghy survey

Post by thinwater »

mikeandrebecca wrote:I love the arch on Desert Star.

We have struggled with so many variations trying to secure it better. We have tried using other lines through blocks led to winches. We run dock lines under it as Drew suggested. Part of the issue with this particular dinghy is that the attachment points on it seem higher than the ones on our old Walker Bay dinghy. Because of this, we lose at least 4-5 inches of height.

I wrote a bit about this on our blog today:

http://www.zerotocruising.com/?p=8883
Aha! I moved the lift points on my tender, which is how I get it so high! The bow attachment is now on the floor, and the stern lower on the transom. I can pull the bow tight against the arms, and the transom just a bit lower (the inside tube is against the davits). Smaller (lower profile) pulleys can help.

Normally you are going to want the transom a few inches lower for drainage, but I don't know about RIBs. I always have mine a little lower than I can haul it in.
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Re: Dinghy survey

Post by fredandkathy »

Thanks for the weight info Mike. I would estimate the 9'6" alum rib I'm considering weighs about the same as yours @ about 100 lbs with the 4 stroke 9.9 only 9 lbs more, so not a lot of difference. I opened the MotorMate crane and set it on the boat. It has not been used before but it will definitely work if I need it. Max lift is 100 lbs. But I REALLY don't want to remove the motor off the dinghy unless I'm storing it and that's why I've been shopping around looking at all the "expensive" models.
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Re: Dinghy survey

Post by Mongoosemagic »

We have a 9'6" Caribe with a Yamaha. It is the max HP reccomended but it is very nice to be able to get the boat up on plane with two people and a load of stuff.
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Re: Dinghy survey

Post by MIDORI »

Here is a photo with the dinghy up while at rest in the mooring field, we leave the motor on.

When traveling, we remove the engine and it is attached to the stern rail. See the motor mount in the photo. When traveling, the dinghy is raised as high as possible, touching the davits with the bottom of the tubes resting on the hull seam, then we use two rachet straps to hold the dinghy tight to the stern rail at the deck level.

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Re: Dinghy survey

Post by mikeandrebecca »

For those who are interested, I posted about our dinghy-carrying solution on our blog today.

http://www.zerotocruising.com/?p=9781
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