Fore / Aft Boat Balance

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AMCarter3
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Fore / Aft Boat Balance

Postby AMCarter3 » Tue Nov 21, 2017 11:06 am

My question is: When your aux. fuel, water and holding tanks are empty, what does your boat's profile look like at the water line? Is it balanced Fore to Aft on the waterline? Or is it stern heavy with the bow riding visibly higher? What does the profile look like when your fuel, water and holding tanks are FULL? Is it bow heavy?

I'm asking because when we replaced our 4 house wetcell batteries last year with four big, heavy (152 lb) AGM's, we noticed a significant (unanticipated) shift in weight balance toward the stern of the boat. The AGM's added a NET total of 368 lbs. at the stern and the bow was riding a good 6" higher at the water line. In my first attempt to re-balance the boat, I put 325 lbs of old chain as ballast in the 2 watertight bow lockers -- 200 lbs in the Port bow and 125 lbs in the Starboard bow. This flattened out the boat’s waterline profile. However, when all 3 bow tanks (fuel, fresh water, black water) are full, the bow was riding LOW... too low for me.

My 2nd attempt to re-balance the boat is a bit more complicated. I recently replaced our CQR anchor with a new Rocna 15 (33 lbs) AND added 175' of 5/16" chain to our anchor rode. Full chain rode is recommended by many seasoned boaters in our area (Pacific Northwest). We now have 325' of anchor chain plus 125' of nylon line. That added 130 lbs of weight at the center of the boat. So, I removed all chain ballast from the Starboard bow (we carry a fairly heavy stuff there -- spare parts, extra props, extra oil, extra 50' shore cable, extra small anchor, etc.). I removed all but 55 lbs of chain ballast from the Port bow. Now, with the water and holding tank empty, the boat sits slightly stern heavy / bow light. With the fuel, water and holding tanks full, it "should" balance out more. But, ideally, I want it to ride flat, not bow heavy.

Any thoughts about this? How do you guys manage fore / aft balance in your boat? Any words of wisdom?
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98
Bellingham WA

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Re: Fore / Aft Boat Balance

Postby duetto » Tue Nov 21, 2017 12:30 pm

hi mac,

remember we have an old boat which i've found to float differently than the 2005 and later boats. we carry a 10'6" rib w/15 hp yamaha 2 stroke and comments are with this on board.

empty our boat is slightly bow down. full fuel and water it sits pretty level. we spend the the winter in the same marina as teamwork a 2005. teamwork sits much lower at the stern than we do.

sounds like you're adding a LOT of weight but not sure i have a good answer. can you get up on plane?
john & diane cummings
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Re: Fore / Aft Boat Balance

Postby deising » Tue Nov 21, 2017 12:42 pm

A few thoughts, Mac; not sure they'll help any.

Our 2006 trims bow heavy by at least 3 inches with full water and fuel, but without the 250 lb dinghy/engine on the davits. When I hoist the dink, it is still slightly bow heavy, but only an inch or so. Dick Tuschick has said that since the stern squats at speed, you are better off bow heavy at rest. I would agree with that from my experience, but we do not go to the high-speed regime very often.

Other knowledgeable PDQ sailors have mentioned that bow heavy is a concern regarding "stuffing a wave." We have been in some steep, standing waves from time to time without any issue other than the severe "hobby-horsing" that occurs. Moderating speed is critical to manage that, but I digress.

Much as we don't like to admit it, I believe the changes made in later years added weight, and the inevitable weight we owners add on for comfortable cruising, have made the performance suffer noticeably in many cases. In your case, you have added a lot of weight in the chain rode and the new batteries. I am sorry not to have any suggestions for changing the trim.
Duane Ising
m/v Diva Di
Punta Gorda, FL
2006 PDQ MV 34 - hull 91, 75HP, 3-blade

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Re: Fore / Aft Boat Balance

Postby AMCarter3 » Wed Nov 22, 2017 2:16 am

Duane,

That's helpful. As of now, our boat is definitely bow LIGHT even with full water and fuel tanks. I think I need to add some of that "ballast" chain back to get to at least level or slightly bow HEAVY with full tanks. I plan to call Dick and discuss this with him.
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98
Bellingham WA

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Re: Fore / Aft Boat Balance

Postby duetto » Wed Nov 22, 2017 8:19 am

mac,

did you add total battery capacity? our golf carts are 65 lbs x 4.
john & diane cummings

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Re: Fore / Aft Boat Balance

Postby thinwater » Wed Nov 22, 2017 12:29 pm

Bear in mind that adding weight to the extreme ends will increase hobby horsing that may be worse than the trim problem. Bow weight should be the absolute last resort, and possibly avoided even then.

Also consider storing parts etc. differently.
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Re: Fore / Aft Boat Balance

Postby AMCarter3 » Thu Nov 23, 2017 12:05 pm

Good questions... couple of responses...

To keep this topic in context, we replaced our 4 wetcell house batteries with 4 heavy AGM's because our objective was to: a) have enough battery capacity to support up to 3 days at anchor without any need to start an engine to recharge (we do not have a genset); and b) be able to charge the house batteries when underway to FULL in about 3 hours. To accomplish this, we had to replace the wetcells with four big, heavy 220 AH Northstar AGM's, AND replace the original port side Hitachi 80 AH alternator with an Electromaax 180 amp Cruiser-Series high capacity alternator, AND add a Sterling 210 Amp 4-stage Smart Charger... plus rewiring with 4-0 cables. That's a lot of weight added... each of the AGM batteries weighs 152 lbs… our wetcells weighed 60 lbs... so the NET weight added added to the stern was 92 lbs per AGM or 368 TOTAL lbs... which caused the bow to rise about 8”.

That's why I've been experimenting with adding chain ballast to our bow lockers. After adding 360 lbs of chain weight to the bows, I was able to flatten the waterline when the fuel, water and holding tanks are relatively FULL. Two observations: 1) the boat did LESS, not more "Hobby Horsing"; 2) we did NOT lose any appreciable speed; and 3) the boat felt more steady in choppy water, less reactive and was more able to punch through 4' chop instead of riding up and over it with the usual loud slam on underside.

Lastly, after reading your comments here and chatting with Dick Tuschick yesterday, I'm going to add enough chain ballast BACK into the bow lockers so the boat will ride slightly bow heavy when the fuel, water and holding tanks are relatively FULL. Thanks for that guidance.

One other question has come up and I'd appreciate any comments on this... for those of you who switched to 4 blade props some time ago, did that generate any perceptible "lift" at the stern? Are you more able to achieve planing in your boat at high speed? I'm asking this because my Yanmar guy tells me putting 4-blade props on boats 30' or under tends to add lift to the stern (in addition to be quieter and producing better performance).
Mac Carter
2006 34' PDQ PowerCat "All Heart"; MV 98
Bellingham WA

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Re: Fore / Aft Boat Balance

Postby thinwater » Thu Nov 23, 2017 5:33 pm

Hobby horsing is very condition-specific. Glad it worked out for you.

I would add that catamarans seem happier and a little faster when trimmed slightly bow-down, unless traveling at very high speed. It is probable that getting back to proper trim had a lot more to do with the reduction in hobby horsing than where the weight was placed. Bow-up is always rough in catamarans.

What is unfortunate is that the battery locker was so far aft.
Writing full time since 2014.

http://sail-delmarva.blogspot.com/2017/ ... store.html
"Keeping a Cruising Boat for Peanuts"
"Singlehanded Sailing for the Coastal Sailor"
"Faster Cruising for the Coastal Sailor"


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